38 BOTANY FOR BEGINNERS. (Ch. X 
thrifty in this situation for a length of time; but as soon as the 
baa plant was placed under “the receiver, it withered and 
ied 
228. The upper surface of leaves is usually of a deeper green, 
and supposed to perform a more important part in respiration, 
than the under surface. The upper surface repels moisture ; 
you may perceive, by examining a cabbage leaf after a shower 
or heavy dew, that the moisture is collected in drops, but has 
no appearance of being absorbed by the leaf. It has been found 
that the leaves of plants, laid with their upper surface upon wa- 
ter, wither almost as soon as if exposed to the air, although the 
leaves of the same plants, placed with their under surfaces up- 
on water, retain their freshness for some days. 
229, But few among the vegetable tribes are destitute either 
of leaves, or green stems, which answer asa substitute. The 
Monotropa, or Indian pipe, is of a pure white, and looks as if 
made of wax. Mushrooms are also destitute of any green 
herbage. It is not known in what manner the deficiency of 
leaves is made up to these vegetables. 
230. The period in which any species of plant unfolds its 
leaves, is termed Frondescence. Linneus paid much atten- 
tion to this subject; he stated as the result of his investigations, 
that the opening of the leaf-buds of the Birch tree, (Betula,) was 
the most proper time for the sowing of barley. The Indians of 
our country had an opinion, that the best time for planting In- 
dian corn, was when the leaves of the white oak first. made 
their appearance; or, according to their expression, are of the 
size of a squirrel’s ears. 
231. One of the most remarkable phenomena of leaves, is 
their trritability, or power of contraction, upon coming in con- 
tact with other substances.’ Compound leaves possess this 
property in the greatest degree; as the foreign sensitive plant, 
and the American sensitive plant : ; these, if the hand is brought 
near them, seem agitated as if with fear ; but as they are desti- 
‘tute of intelligence, we must attribute this phenomenon to some 
physical cause, perhaps the warmth of the hand, which produces 
the contractions and dilatations of the leaves. 
232. The effect of tight upon leaves is very apparent, plants 
being almost uniformly found to present their upper surfaces 
228. In what respects co the upper and under surfaces of leaves 
differ ? 
229. What plants are destitute of leaves? 
230. What is meant by the term Frondescence ? 
231. What is said of the irritability of leaves? 
232. What is said of the effect of light upon leaves? 
