sentence-transformers/squad huggingface dataset:
Passage: Heartwood is often visually distinct from the living sapwood, and can be distinguished in a cross-section where the boundary will tend to follow the growth rings. For example, it is sometimes much darker. However, other processes such as decay or insect invasion can also discolor wood, even in woody plants that do not form heartwood, which may lead to confusion.

Question: In what part of a tree's cross-section is heartwood visible?

Question: What simple color distinction can heartwood have that makes it stand out from living wood in a tree?

Question: Along with insect infestation, what process can discolor wood and make it look like heartwood?

Question: What kind of plants never form heartwood?

Question: What is the living wood in a tree called?
Passage: Sapwood (or alburnum) is the younger, outermost wood; in the growing tree it is living wood, and its principal functions are to conduct water from the roots to the leaves and to store up and give back according to the season the reserves prepared in the leaves. However, by the time they become competent to conduct water, all xylem tracheids and vessels have lost their cytoplasm and the cells are therefore functionally dead. All wood in a tree is first formed as sapwood. The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests. Sometimes trees (of species that do form heartwood) grown in the open may become of considerable size, 30 cm or more in diameter, before any heartwood begins to form, for example, in second-growth hickory, or open-grown pines.

Question: What term is interchangeable with "sapwood"?

Question: Is sapwood the younger or older wood in a tree?

Question: What essential liquid is the sapwood tasked with carrying around a tree?

Question: How much of the wood in a tree is sapwood at some point in its life?

Question: Does a tree growing quickly out in the open have thinner or thicker sapwood for its size than the same kind of tree in a dense forest?
Passage: The term heartwood derives solely from its position and not from any vital importance to the tree. This is evidenced by the fact that a tree can thrive with its heart completely decayed. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut, black locust, mulberry, osage-orange, and sassafras, while in maple, ash, hickory, hackberry, beech, and pine, thick sapwood is the rule. Others never form heartwood.

Question: If a tree starts forming heartwood right away, will its sapwood layer be thin or thick?

Question: What property of heartwood that has nothing to do with how important it is to trees got it its name?

Question: Does a beech tree usually have thin or thick sapwood?

Question: Does a sassafras tree typically have a thin or thick sapwood layer?

Question: Would a thin or a thick sapwood layer be found in a pine tree?
Passage: No definite relation exists between the annual rings of growth and the amount of sapwood. Within the same species the cross-sectional area of the sapwood is very roughly proportional to the size of the crown of the tree. If the rings are narrow, more of them are required than where they are wide. As the tree gets larger, the sapwood must necessarily become thinner or increase materially in volume. Sapwood is thicker in the upper portion of the trunk of a tree than near the base, because the age and the diameter of the upper sections are less.

Question: What part of a tree is the cross-sectional area of the sapwood approximately proportional to?

Question: Are more rings necessary if they're narrow or wide?

Question: As a tree grows bigger, if the sapwood layer doesn't increase in volume, what will it become?

Question: In what part of the tree trunk is the sapwood layer thinnest?

Question: Along with the smaller diameter of the upper trunk, what factor leads to thinner sapwood higher up a tree?
Passage: When a tree is very young it is covered with limbs almost, if not entirely, to the ground, but as it grows older some or all of them will eventually die and are either broken off or fall off. Subsequent growth of wood may completely conceal the stubs which will however remain as knots. No matter how smooth and clear a log is on the outside, it is more or less knotty near the middle. Consequently, the sapwood of an old tree, and particularly of a forest-grown tree, will be freer from knots than the inner heartwood. Since in most uses of wood, knots are defects that weaken the timber and interfere with its ease of working and other properties, it follows that a given piece of sapwood, because of its position in the tree, may well be stronger than a piece of heartwood from the same tree.

Question: What usually covers the whole trunk of a very young tree?

Question: What evidence of the stubs of the limbs a tree loses can always be seen in the wood?

Question: In a very old tree, are you more likely to find a lot of knots in the heartwood or the sapwood?

Question: What hides the stubs of a tree's lost limbs from being visible later in its life?

Question: Since knots are defects that weaken lumber, would the heartwood or the sapwood from the same tree be stronger?
Passage: It is remarkable that the inner heartwood of old trees remains as sound as it usually does, since in many cases it is hundreds, and in a few instances thousands, of years old. Every broken limb or root, or deep wound from fire, insects, or falling timber, may afford an entrance for decay, which, once started, may penetrate to all parts of the trunk. The larvae of many insects bore into the trees and their tunnels remain indefinitely as sources of weakness. Whatever advantages, however, that sapwood may have in this connection are due solely to its relative age and position.

Question: What do broken limbs and deep wounds open a door for in a tree?

Question: Decay can spread to all of what part of a tree?

Question: What growth stage of insects bore holes into trees?

Question: What part of a tree often stays impressively sound even when hundreds or thousands of years old?

Question: What evidence do some insect larvae leave in a tree forever?
Passage: If a tree grows all its life in the open and the conditions of soil and site remain unchanged, it will make its most rapid growth in youth, and gradually decline. The annual rings of growth are for many years quite wide, but later they become narrower and narrower. Since each succeeding ring is laid down on the outside of the wood previously formed, it follows that unless a tree materially increases its production of wood from year to year, the rings must necessarily become thinner as the trunk gets wider. As a tree reaches maturity its crown becomes more open and the annual wood production is lessened, thereby reducing still more the width of the growth rings. In the case of forest-grown trees so much depends upon the competition of the trees in their struggle for light and nourishment that periods of rapid and slow growth may alternate. Some trees, such as southern oaks, maintain the same width of ring for hundreds of years. Upon the whole, however, as a tree gets larger in diameter the width of the growth rings decreases.

Question: In what stage of its life does a tree usually grow the fastest?

Question: As a tree ages, do its growth rings usually get wider or narrower?

Question: What part of a tree opens and spreads out more as it matures?

Question: Is wood production of a tree lessened or increased as it ages?

Question: Along with nutrients, what do trees growing in forests have to compete for?
Passage: Different pieces of wood cut from a large tree may differ decidedly, particularly if the tree is big and mature. In some trees, the wood laid on late in the life of a tree is softer, lighter, weaker, and more even-textured than that produced earlier, but in other trees, the reverse applies. This may or may not correspond to heartwood and sapwood. In a large log the sapwood, because of the time in the life of the tree when it was grown, may be inferior in hardness, strength, and toughness to equally sound heartwood from the same log. In a smaller tree, the reverse may be true.

Question: When a big tree is cut up, will the pieces of wood differ or all be the same?

Question: In a large log, will the heartwood or sapwood usually be stronger and tougher?

Question: If you need really hard, strong wood from a small tree, would it likely be better to use the heartwood or sapwood?

Question: Besides big trees, what trees are more likely to have a range of different kinds of wood?
Passage: In species which show a distinct difference between heartwood and sapwood the natural color of heartwood is usually darker than that of the sapwood, and very frequently the contrast is conspicuous (see section of yew log above). This is produced by deposits in the heartwood of chemical substances, so that a dramatic color difference does not mean a dramatic difference in the mechanical properties of heartwood and sapwood, although there may be a dramatic chemical difference.

Question: When trees have a visible difference in color between sapwood and heartwood, which is darker?

Question: What is deposited naturally in heartwood that changes its color?

Question: Is the color difference between heartwood and sapwood usually very subtle or conspicuous?

Question: What type of properties of heartwood and sapwood is often the same even if their colors are very different?

Question: Although heartwood and sapwood might be similar mechanically, if their colors are very different, what other type of difference would they have?
Passage: Some experiments on very resinous Longleaf Pine specimens indicate an increase in strength, due to the resin which increases the strength when dry. Such resin-saturated heartwood is called "fat lighter". Structures built of fat lighter are almost impervious to rot and termites; however they are very flammable. Stumps of old longleaf pines are often dug, split into small pieces and sold as kindling for fires. Stumps thus dug may actually remain a century or more since being cut. Spruce impregnated with crude resin and dried is also greatly increased in strength thereby.

Question: What type of tree has resin that makes it stronger when it dries?

Question: What's the funny name for resin-saturated heartwood?

Question: What is fat lighter practically impervious to in addition to termites?

Question: If spruce is shot full of crude resin and dried, which of its properties is increased?

Question: Since it's highly flammable, what do people often use little pieces of longleaf pine tree stumps for?
Passage: Since the latewood of a growth ring is usually darker in color than the earlywood, this fact may be used in judging the density, and therefore the hardness and strength of the material. This is particularly the case with coniferous woods. In ring-porous woods the vessels of the early wood not infrequently appear on a finished surface as darker than the denser latewood, though on cross sections of heartwood the reverse is commonly true. Except in the manner just stated the color of wood is no indication of strength.

Question: Which of the wood in a growth ring is usually darker?

Question: Which property of a tree's wood that gives clues about its strength and hardness can be judged by it's color?

Question: What category of trees show this difference greatly?

Question: What type of woods might sometimes appear to have darker earlywood on a finished surface?

Question: With the exception of earlywood/latewood difference in some types of trees, how much of an indication of strength is a wood's color?
Passage: Abnormal discoloration of wood often denotes a diseased condition, indicating unsoundness. The black check in western hemlock is the result of insect attacks. The reddish-brown streaks so common in hickory and certain other woods are mostly the result of injury by birds. The discoloration is merely an indication of an injury, and in all probability does not of itself affect the properties of the wood. Certain rot-producing fungi impart to wood characteristic colors which thus become symptomatic of weakness; however an attractive effect known as spalting produced by this process is often considered a desirable characteristic. Ordinary sap-staining is due to fungal growth, but does not necessarily produce a weakening effect.

Question: What condition does an abnormal color usually indicate in wood?

Question: What other property can you assume of wood that is diseased?

Question: What causes the black checked pattern in the wood of western hemlocks?

Question: What animals cause the reddish-brown streaks of color in hickory wood?

Question: What's the name for the pretty coloring effect caused in some wood by rot-producing fungi?
Passage: In heartwood it occurs only in the first and last forms. Wood that is thoroughly air-dried retains 8–16% of the water in the cell walls, and none, or practically none, in the other forms. Even oven-dried wood retains a small percentage of moisture, but for all except chemical purposes, may be considered absolutely dry.

Question: What does wood retain in its cell walls despite being air-dried?

Question: Air-dried wood keeps up to what percentage of the water in its cell walls?

Question: What kind of dried wood retains a small quantity of water but is considered absolutely dry?
Passage: The general effect of the water content upon the wood substance is to render it softer and more pliable. A similar effect of common observation is in the softening action of water on rawhide, paper, or cloth. Within certain limits, the greater the water content, the greater its softening effect.

Question: Often the water in wood makes it more pliable and what else?

Question: What material sometimes used for dog chews reacts similarly to wood because of its water content?

Question: What material we use to write or print on, like wood, becomes softer and more pliable when wet?

Question: When water content increases within certain limits in wood, does is have a less or greater softening effect?

Question: What type of action does water create in cloth?
Passage: Drying produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry spruce block 5 cm in section, which will sustain a permanent load four times as great as a green (undried) block of the same size will.

Question: What will drying often increase in wood?

Question: What color is also used interchangeably with "undried" for wood?

Question: What type of wood can hold four times as much of a load when dried?
Passage: The greatest strength increase due to drying is in the ultimate crushing strength, and strength at elastic limit in endwise compression; these are followed by the modulus of rupture, and stress at elastic limit in cross-bending, while the modulus of elasticity is least affected.

Question: What type of "ultimate" strength is one of the two types increased the most by drying wood?

Question: What property of wood is least affected by drying?

Question: Is strength at elastic limit in endwise compression or stress at elastic limit in cross-bending increased more by drying wood?

Question: Is the strength of the modulus of rupture or elasticity increased more when wood is dried?
Passage: Wood is a heterogeneous, hygroscopic, cellular and anisotropic material. It consists of cells, and the cell walls are composed of micro-fibrils of cellulose (40% – 50%) and hemicellulose (15% – 25%) impregnated with lignin (15% – 30%).

Question: Along with hygroscopic, cellular, and anisotropic, how is the material of wood described?

Question: What does wood consist of?

Question: What part of wood's cells are composed of cellulose and hemicellulose?

Question: What makes up 40-50% of the cell walls in wood?

Question: What substance is hemicellulose impregnated with?
Passage: In coniferous or softwood species the wood cells are mostly of one kind, tracheids, and as a result the material is much more uniform in structure than that of most hardwoods. There are no vessels ("pores") in coniferous wood such as one sees so prominently in oak and ash, for example.

Question: What type of cells makes up most wood cells in coniferous trees?

Question: Are hardwood or softwood species more uniform in structure?

Question: What are the visible vessels in hardwoods commonly called?

Question: What hardwood that starts with the letter "O" would have pores?

Question: Besides oak, what's an example of a hardwood with prominent pores?
Passage: The structure of hardwoods is more complex. The water conducting capability is mostly taken care of by vessels: in some cases (oak, chestnut, ash) these are quite large and distinct, in others (buckeye, poplar, willow) too small to be seen without a hand lens. In discussing such woods it is customary to divide them into two large classes, ring-porous and diffuse-porous.

Question: Is the structure of hardwood simple or complex?

Question: What handles most of the water conduction in hardwoods?

Question: Are the vessels in chestnut wood large or small?

Question: In wood from a willow tree, what would you need to use to see the tiny vessels?

Question: Besides ring-porous, what's the other class hardwoods are often divided into?
Passage: In ring-porous species, such as ash, black locust, catalpa, chestnut, elm, hickory, mulberry, and oak, the larger vessels or pores (as cross sections of vessels are called) are localised in the part of the growth ring formed in spring, thus forming a region of more or less open and porous tissue. The rest of the ring, produced in summer, is made up of smaller vessels and a much greater proportion of wood fibers. These fibers are the elements which give strength and toughness to wood, while the vessels are a source of weakness.[citation needed]

Question: What species of hardwood are hickory and mulberry trees?

Question: In what season do the growth-rings of ring-porous species form with larger vessels localized?

Question: In what season does the part of the growth-ring with smaller vessels form in ring-porous species?

Question: What fibers does the summer's section of growth-ring have more of?

Question: Along with strength, what property do wood fibers lend to wood?
Passage: In diffuse-porous woods the pores are evenly sized so that the water conducting capability is scattered throughout the growth ring instead of being collected in a band or row. Examples of this kind of wood are alder, basswood,[citation needed] birch, buckeye, maple, willow,and the Populus species such as aspen, cottonwood and poplar. Some species, such as walnut and cherry, are on the border between the two classes, forming an intermediate group.[citation needed]

Question: What kind of woods have pores that are uniformly sized?

Question: What species do aspen, cottonwood, and poplar trees belong to?

Question: With walnut, what's another tree in the intermediate group?

Question: What capability is spread through the growth ring in ring-porous species?

Question: Is maple wood diffuse-porous or ring-porous?
Passage: In temperate softwoods there often is a marked difference between latewood and earlywood. The latewood will be denser than that formed early in the season. When examined under a microscope the cells of dense latewood are seen to be very thick-walled and with very small cell cavities, while those formed first in the season have thin walls and large cell cavities. The strength is in the walls, not the cavities. Hence the greater the proportion of latewood the greater the density and strength. In choosing a piece of pine where strength or stiffness is the important consideration, the principal thing to observe is the comparative amounts of earlywood and latewood. The width of ring is not nearly so important as the proportion and nature of the latewood in the ring.

Question: What kind of softwoods often have significant differences in their earlywood and latewood?

Question: Is latewood denser or less dense than earlywood?

Question: Does strength come from the walls or cavities of wood cells?

Question: Are the cell walls of earlywood thick or thin?

Question: What general size are the cavities in the cells of very dense latewood?
Passage: If a heavy piece of pine is compared with a lightweight piece it will be seen at once that the heavier one contains a larger proportion of latewood than the other, and is therefore showing more clearly demarcated growth rings. In white pines there is not much contrast between the different parts of the ring, and as a result the wood is very uniform in texture and is easy to work. In hard pines, on the other hand, the latewood is very dense and is deep-colored, presenting a very decided contrast to the soft, straw-colored earlywood.

Question: Comparing a heavy and a lightweight piece of wood from a pine, which would have a greater proportion of latewood?

Question: What feature of a piece of pine with more latewood would be more clear and pronounced?

Question: What type of tree has very little contrast between parts of its growth rings?

Question: Is white pine easy or difficult to work with because of its texture?

Question: What kind of pines have very deep, darkly colored hardwood that stands out against the light earlywood?
Passage: It is not only the proportion of latewood, but also its quality, that counts. In specimens that show a very large proportion of latewood it may be noticeably more porous and weigh considerably less than the latewood in pieces that contain but little. One can judge comparative density, and therefore to some extent strength, by visual inspection.

Question: Having a high proportion of latewood isn't all that matters; what else is important?

Question: What can we judge in wood just by looking at it?

Question: What property of wood could we project some indication of by looking at its density?

Question: What could we call some specimens with a high proportion of latewood that explains why they weigh less than specimens with much less latewood?
Passage: No satisfactory explanation can as yet be given for the exact mechanisms determining the formation of earlywood and latewood. Several factors may be involved. In conifers, at least, rate of growth alone does not determine the proportion of the two portions of the ring, for in some cases the wood of slow growth is very hard and heavy, while in others the opposite is true. The quality of the site where the tree grows undoubtedly affects the character of the wood formed, though it is not possible to formulate a rule governing it. In general, however, it may be said that where strength or ease of working is essential, woods of moderate to slow growth should be chosen.

Question: What facet of wood is affected to some degree by the place where the tree grows?

Question: If you want wood that's easy to work with, what kind of growth would you want the tree to have?

Question: What species of tree can be said to growth ring proportions that aren't determined just by their rate of growth?

Question: What counterpart of earlywood are scientists still trying to explain the formation of?

Question: While there is some relationship between where and how a tree grows, what can't anyone formulate to govern it?
Passage: In ring-porous woods each season's growth is always well defined, because the large pores formed early in the season abut on the denser tissue of the year before.

Question: What kind of woods always have very clearly marked seasonal growth?

Question: What size pores form early in ring-porous woods' growing season?

Question: When does the denser tissue the new pores abut come from?