Human Physiology. in 



sensitiveness, choice, and intelligence. The mimosa closes its 

 leaves at a touch. A sensitive Australian plant closes even 

 at the approach of any one. Nearly all, without a mistake, 

 send their roots downward and their stems towards the light. 

 The roots of the rose grow toward water, curiously turning 

 around obstacles. The hop and the tendrils of vines seem to 

 reach out for support, and to be impelled or attracted towards 

 objects near them. Some plants close their flowers against the 

 heat of the sun ; others carefully fold them up at night as if to 

 guard against the cold. 



The tendency of most plants toward the light is very strik- 

 ing. Some turn their leaves, some their flowers toward the 

 point where it is strongest. A grape vine growing in the shade 

 of tall trees climbs to their tops before it sends out its branches 

 and leaves. Trees growing with others, for the same reason 

 shoot up straight and slender. Bend down the stalk of the 

 mullein at a sharp angle, and in a few days it will have made 

 a graceful bend so as to point again to the zenith. If potatoes 

 are allowed to sprout in a cellar, the sprouts grow toward the 

 light, if it be from ever so small a crevice, in long slender 

 stalks, which may be at an angle of 45 degrees or less from 

 the horizontal. Plants bend toward white light and from red. 

 Red keeps flowers and fruit from decay. I have seen a line of 

 great trees by the road-side growing with three-fourths of the 

 bulk of their branches over the road, apparently more for air 

 than sun, and as if to avoid the neighbourhood of much smaller 

 trees growing near them. So in a clump of larches, the 

 branches are long only on the circumference of the group. 



Plants have a skin and epidermis like animals; and this is, 

 like theirs, converted into scales, hair, sharp spines for defence 

 against climbers, as one sees on the acacia, &c. On the leaf 

 skin there are pores, in some cases 90,000 to the square inch, 

 which regulate respiration and evaporation, open or close at 

 ueed, some being retractile drawing in like a telescope. 



