### definite unit:

Natural plant tissue
* All plant tissues are acidic to some degree, and some are much more so than others.
* Plant tissue consists of complex carbohydrates synthesized from simple carbohydrates.
* Plant tissue is damaged as a result of plant fluid removal and injection of toxic substances
  - natural object
  - tissues accumulate salts from lower soil horizons
* Plant tissues are characterized and classified according to their structure and function
  - soft and often flaccid, even under conditions of low stress for water
  - the only source of nitrogen for animals
  - very brittle, especially under conditions of low stress for water
  - become sensitive to environmental stresses such as drought and heat
  - harbor fascinating gaseous microenvironments
  - undergo a slimy disintegration
  - vary gTeatly in their chemical com- position and availability
* Some plant tissue contains chemical compounds
  - more toxic compounds

### definite unit:

Natural pollen tube
* A pollen tube natural object
* Pollen tube enters the female gametophyte through an opening called the micropyle
  - grows down stigma, sperm nuclei enter female gametophyte
* Pollen tubes are an excellent model for the understanding of plant cell behavior
  - formed through the style and extend from the stigma to the ovary
  - very sensitive to sugars and grow in their direc- tion
  - begin to form soon after pollen grains lodge on the stigma
  - germinate from the pollen grains and grow toward
  - grow down the hollow center of the style as they head toward the ovary
* Some pollen tubes grow into female gametophytes
* Some pollen tubes penetrate silk tissue

### definite unit:

Natural pycnidium
* A pycnidium natural object
* Pycnidia appear as black specks in the infected areas.
* Pycnidia are asexual fruiting structures associated with certain fungi
  - light to dark brown in color and partially embedded within plant tissue
  - most noticeable following a period of dew or rain
  - tiny, orange spore-cases that characterize spreading chestnut blight
  - contain short, simple conidiophores that produce the fungal spores
  - develop within the infected tissue
  - occur in clusters or singly on stems and needles
  - produce spores during wet weather, which are then spread by splashing water and wind
  - usually form in rows in the dead parts of leaves

### definite unit:

Natural radiator
* A radiator natural object
* Most radiators have bleeder value on the outlet end of the radiator.
* Radiator cast aluminum uplighter made to withstand the elements.
* Radiators are a common way to keep buildings in cold environments
  - heaters
* Radiators are located in apartment buildings
  - apartments
  - cars
  - rooms
  - trucks
  - mechanisms
  - natural objects
* Radiators are part of automobiles
  - heating systems
  - the most common source of heat transfer, but radiant loops are gaining popularity
  - used to heat the building, The energy source is oil
  - can also lose a great deal of heat to the walls they are installed against
* Some radiators are used to cool things , such as a car engine
  - heat things , such as a house
  - have valves to turn the heat on and off.
  * A 'radiator' device used to move heat from one location to another location. Some radiators are used to cool things, such as a car engine

Natural sclerotium
* A sclerotium natural object
* Sclerotia are highly resistant structures and survive for long periods in soil
  - have a hard, black exterior rind with a white to light beige interior
* Sclerotium lacks fruiting structures and spores.