CONDITIONS MOST FAVORABLE FOR VEGETABLE ACTIVITY. 41 
For others it does not exceed 70°. In a miscellaneous collection, some, of 
course, would suffer. Vegetable activity may be measured also by growth and 
movements. A description of apparatus devised by Dr. Wilson was given, and 
a picture of the same thrown upon the screen. It consisted essentially of a 
generator whence gases could be fed to a receptacle containing plants or germi- 
nating seeds, and an aspirator for withdrawing from this the products of growth 
through liquids which would attract and detain certain elements, as carbonic acid. 
Thus a stream of hydrogen could be fed to germinating seeds. Carbonic acid 
was found to be a product of the growth, and as no oxygen was given the plant, 
it must have come from the tearing asunder of the molecules composing the 
seeds. This was first tried in Professor Sach's laboratory. Apparatus to measure 
growth was then explained. A delicately weighted lever attached to the growing 
tip of a plant rested at the end against a cylinder of blackened paper turned by 
clock-work. As the plant elongated in growth the end of the lever would de- 
scend and indicate the rapidity of growth by the lines on the paper. Leaving 
out of view slight diurnal oscillations of growth not yet accounted for, we find 
that at the optimum temperature growth is accelerated, and that light slightly 
retards the same. Another and perhaps better way of testing vegetable activity 
was by measuring movements made by plants in growing. This was illustrated 
by views of various plants on the screen. On the hop vine the flexible end of the 
stem twists about a support, and thus raises itself into light and air with a slight 
expenditure of woody tissue, the whole revolution made is in from two to four 
hours under favorable conditions. The morning-glory has a long projecting arm 
which sweeps around and clings to support. 
The jasmine solanum twists its leafstalks about other plants, and so climbs 
upward. The passion vine was shown to have tendrils, which were modified 
forms of branches, moving and sensitive. Virginia creeper has tendrils with a 
disk at the end, which fastens itself to support. The activity of these tendrils is 
increased in darkness, i. e. , the plant is negatively heliotropic. Another form 
was shown in the leaf of the nepenthes, where a tendril was found between the 
blade of the leaf and the pitcher. In conclusion of this part of the subject the 
lecturer said that the observations made prove that the most favorable conditions 
for vegetable activity are, (i) supply of proper amount of the gases; (2) sufficient 
moisture; (3) best degree of heat; (4) requisite kind and amount of food. 
This last point leads to a consideration of those plants which obtain part of 
their nitrogen from animal food. These may be divided into two classes : First, 
those which have fly-catching traps, as the drosera, where the leaf is covered with 
tentacles of various lengths tipped with a viscid liquid. These are not sensitive 
to straw or metal, but place on them a bit of beef or albuminous substance and 
they will close over it, and after a few days it will have disappeared. The dionea 
has at the end of its leaf-blade two valves bearing three sensitive bristles. The 
edge is also fringed with hairs. If an insect touches this the valves close, the 
bristles on the edge interlock loosely ; if the insect be small it escapes ; if large, 
t is retained, a glairy fluid is exuded and the fly is digested as food is digested in 
