The sun., 1888-10-28

sive growth OF tissues: thus the tissues In the
petioles OF clematls thicken after they have
elung to q foreign body. In AUDclopsis hedera-
ced the tendrils do not form pads until they
have met the surface Of n wall. The irritation
set up by ants determines the hypcrtrophied
condition o; stipules in Acacia sp',grocephd!uS,
and OF stems In N7p,ecodiurn. The epidermal
cells OF aerial roots In the ivy and in orchids.
elongate into adhesive hairs from the mechan-
ical irrita alton OF contact with foreign body.
This action OF these cells is probably
aided by moisture and the lessened
supply OF light which they receive
on account OF being on the under
side OF the stem. II Is n common thing for leaf
buds to be arrested in development, or meta
morphosed in form, by insects punctLring
them to deposit their eggs. Experiments have
shown that trees will develop wood in par
ticular directions to meet strains imposed
upon them; and cactuaes, says Mr.. Herbert
Spencer. develop woody tissues to enable them
to bear special strains. Stems which have
to support the weight OF flowers and fruit,
develop various kinds OF strong supporting
tissues to meet tho call upon them, A pear or
ample which hangs straight downward grows
symmetrically around the stalk. but II 1t
projects obliouely from the branch 1t ennrges
along the upper side, to meet the UNEQUAL
strain upon it, Thus, says Prof. Henslow. we
have abundant proof OF the responsive power
OF protoplasm to build UP tissues wherever
they are required" and there is. In fact, an
abundance OF evidence to prove that many
organs Of plant. II subjected to irritation can
respond to It, and not only increase in size by
hypertrophy, but materially alter their
anatomical structure and develop now pro-
ccssea. Secondly. that these altered states, II
tho irritation be persisted In, may become
hereditary"
Above all other parts Of plants. flowers are
most keenly sensitive to stimuli We all ac-
customed to the regular opening and closing Of
many common flowers rs the daylight comes
and goes, while tho styles, stigmas, fllaments,
and anthers Of many others exhibit spontane-
GUS movements. This sensitiveness to all kinds
OF stimuli causes flowers to vary with especial
ease and Prof. Henslow concludes that "the
forms and structures Of flowers are the direct
outcome OF the responsive powers OF protoplasm
to external stimuli" and II we may admit the
existence OF this adaptability to strains and
other external forces and that the various
structures Of flowers will grow in response to
them and develop themselves accordingly. we
have clue to the Interpretation Of every one
Of the most diverse forms which may be found
in flowers adapted to insect agency"
Our author tells US that the idoa that insects
might be directly responsible for many pecu-
liarities In the structure OF flowers first oc-
Cured to him on watching bee hanging from
the dependent stamens Of blossom. 1t struck
him that the way in which the stamens hung
down might possibly be an hereditary result OF
tho repeated application OF the weight of bees.
The development of this idea brought him at
last to the conclusion quoted above. viz. that
all those flowers which are perfectly adapted
to insect agency. are the outcome OF all tho
forces which the insect has either brought into
play by his immediate presence or forced into
action by his search for honey or pollen. |
Though there are innumerable forms OF irreg-
ular corolas, yet certain principles. Prof. Hen
slow contends, will always be found to govern
them. The side OF tho corolla upon which |
the insect rests. or throws its weight, In its
efforts to extract the honey. is always enlarged.
takes place where the greatest
strain occurs, as is well illustrated in the slip
pc r-shaped flowers OF Calceolaria and Cypripe-
dunn. II no moro than the head of an insect
enter the flower. then the corolla shapes itself
10 lt 1t. as in snowberry. scrophularia. and |
epipactis. which admit only the heads Of wasps. |
their regular visitors. Lips OF various kinds,
keels. and often the wing petals where they |
help to support the insect can be accounted |
Tor by tho effect Of tho weight OF the insect de-
flow of nutrIment to the parts de- |
handing it. with tho result that they grow |
INTO the required forms. The honeysuckle is |
II almost regular form. according to this
heory. because. being visited by lepidopter-
ous insects which hover In front Of It without |
it has had no exciting cause to in
luce irregularity in the corolla but the singu-
ar length OF its tube is to be attributed to
growth in response to tho constant irritation
If probing by the long tongues OF butterflies
md moths Thus the great diversity OF floral
structures corresponds to an equal diversity In
he insect world. Tho flower which Is visited
~ many insects will assume form the result
II the various forces brought to bear upon It,
while II visited BY few insects it will shape it.
'elf to answer the requirements OF those few.
To similar causes the writer would attribute
he existence OF all floral attributes. such as
lairs. glutinous secretions, &c. According to
lis view they are all the result OF irritation,
Produced by the actual presence Of insects.
ather than processes developed by tho flower
o forbid the intrusion Of unwelcome visitors
Thus while many regular flowers which can bo
approached on every side have developed horl-
;ontal hairs all around the entrance to the tube
II the corolla, flowers which are irregular, and
approached from ono side only. develop them
nly on the anterior side. III we watch the
labits Of insects with their tongues, We may
asily see how they irritate tho various parts
" licking them. not solely where tho honey is
ecreted, but the 1laments, &C. Thus Muller
ften watched Rhingia rostrata licking the
taminal hairs OF Ver5ascun phoniceun,. and in
many cases the hairs on the fllaments offer
oothold to the insects while visiting the fiow-
rs, as in species Of Mullen; such hairs, II
~ theory be true, being the actual result OF
he insects clutching the alaments or rubbing
hem with their claws. In Centaurra tho cpl
ermal cells have produced projecting pro-
esses Just where the proboscs rubs against
hem in searching for honey" That mechanl-
al irritation can give rise to similar growths
, other parts OF the plant Is shown by the oc-
urrence OF such hairs In the interior. as also
n the outside OF many OF the gals produced
, different plants by the deposition there of
lsects' eggs But for those appendages which
ppear on the stems or leaves of plants ap-
arently without any irritation to produce
1em. Prof. Henslow admits that his theory
i'll not account. He still. however. holds
rmly to the belief that the cause is to be
ought for In some direct action OF the enyi-
onment upon the plant. We know at least
lat certain conditions. such as growth In