68 
by which the cell takes in the sap, retains what it needs, and then 
gets rid of the water and the dissolved substances which it does not 
need. Thus the cell wall thickens and enlarges and the contents of 
the cell increase. The sap enters the cell from that side of the cell 
which is turned toward the interior of the plant or adjacent cells, 
and the rejected water penetrates the cell wall on that side of the cell 
which is exposed to the open air, and especially on that side exposed 
to the sunshine; having reached the outer surface of the cell wall on 
this side of the cell it is then evaporated. This endosmosis by which 
the sap enters the cell on one side, and the exosmosis by which it leaves 
the cell on the opposite side, constitute the fundamental mechanics 
of all vital activities; the chemistry of animal and vegetable hfe 
differs from the ordinary chemistry. of the laboratory in that the 
former studies the behavior of the cell wall toward the molecule, 
while the latter studies the behavior of the molecule toward the 
molecule. An interesting contribution to the development of this 
idea of the chemistry of the action of the cell is contained in two 
papers by Miss Abbott (now Mrs. Michael, of Philadelphia), pub- 
lished in 1887 in the Journal of the Franklin Institute; from the 
second paper I take the following extract: 
The botanical classifications based upon morphology are so fre- 
quently unsatisfactory that efforts in some directions have been made 
to introduce other methods. 
There has been comparatively little study of the chemical principles 
of plants from a purely botanical view. It promises to become a new 
field of research. 
The Leguminose are conspicuous as furnishing us with important 
dyes, e. g., indigo, logwood, catechin. The former is obtained prin- 
cipally from different species of the genus /ndigofera, and logwood 
from the Zamatoxylon campechianum, but catechin from the Acacia 
catechu. 
The discovery of hematoxylon in the Saraca indica illustrates very 
well how this plant, in its chemical as well as botanical character, is 
related to the Zwmatoxylon campechianum; also, I found a sub- 
stance like catechin in the Savaca. This compound is found in the 
Acacias, to which class Saraca is related by its chemical position as 
well as botanically. Saponin is found in both of these plants, as well 
as in many other plants of the Leguminose. The Leguminosze come 
under the middle plane of multiplicity of floral elements, and the 
presence of saponin in these plants was to be expected. * * * 
From many of the facts above stated, it may be inferred that the 
chemical compounds of plants do not occur at random. Each stage 
of growth and development has its own particular chemistry. 
