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 life 

 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 Leguminosse 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 Indigofera, and logwood 

 from the Hcematoxylon campechianum^ but catechin from the Acacia 

 catecliH. 



The discovery of hrematoxylon in the Saraca indica illustrates very 

 ivell hoAv this plant, in its chemical as well as botanical character, is 

 related to the Harndtoxylon campechianum; also, I found a sub- 

 stance like catechin in the Saraca. 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 Leguminosfp. The Leguminosa' 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. 



