PHYSIOLOGY. 975 
vun straight forward, emitting single fascicles on its 
sides, then we have a veined leaf. If there are on 
the margins of the leaf numerous anastomoses, sucht 
a leaf is then called folium integerrimum. But if the 
fascicles spread in small unconnected branches to- 
wards the margin, the leaf becomes, according to 
circumstances, serrated, dentated, crenate, and so 
orth. 
These fascicles of vessels in leaves are composed 
of air and adducent vessels. The net-work they form, 
is in both its surfaces covered with cellular texture, 
in which the reducent vessels lie. And the external 
membrane or cutis which on both sides invests the 
cellular texture, is provided with innumerable lym- 
phatic vessels, (§ 235), and their exhaling pores. 
The footstalk of leaves resembles in its structure 
that of the stem, except that the air-vessels on its 
base by their convolutions form a knot, which 
serves for the evolution of the bud, their direction 
having been changed. In sessile leaves, or such, 
which want the footstalk, we seldom find such a 
knot formed by vessels, and therefore they will not 
always produce buds at their base. 
Sy Arik at 
Of all the parts of plants, the leaves shew the 
most singular irritability ; and particularly the com- 
pound leaves of many plants are very susceptible of 
stimuli. Merely by touching the leaves of Mimosa 
pudica, sensitiva, casta, Oxalis sensitiva ; Smithia sen- 
sitive and many others, they instantly contract 
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