ASSIMILATION. 119 



the plant ; for it disappears from the leaves and other or- 

 gans of plants when their vitality is exhausted. A partial 

 oxydation of this starch produces the chromule, and as the 

 oxydation increases, gum and sugar. This oxydating or con- 

 suming process necessarily partially arrests the further de- 

 velopment of the organs; the growth of the plant is to 

 some extent stopped, the petiole assumes the form of a fila- 

 ment, and the lamina being contracted into an anther, a 

 stamen is produced. 



The change, however, from the de-oxydating to the oxy- 

 dating process is undoubtedly gradual. Hence those 

 transition forms between the leaf and stamen, which so 

 satisfactorily prove that the two are but one and the same 

 organ. 



We have already shown that the fibro-vascular system 

 of plants and the blood vessels of animals are subordinate 

 in function to the cells with which their terminal capillary 

 ramifications finally communicate, and that it is in these 

 cells that the changes take place by -which the fluid is trans- 

 muted into the various products necessary to the nutri- 

 tion of the organism. The sap of plants in traversing the 

 tissues is elaborated into starch, chlorophyl, chromule, 

 gum, and sugar; and, in like manner, the blood which is 

 conducted by means of the capillaries, not only through all 

 the softer parts of the framework, but even into the solid 

 substance of the bones, gives up its constituents to the 

 several tissues which it traverses, the cells attracting from 

 it their own proper formative material. Its constituents 

 are thus transmuted into bile, saliva, tears, and various 

 coloring matters. The plumage of birds and the hues 

 of flowers are alike the results of this selecting power exer- 

 cised by the cells on the constituents of the nutrient fluid. 



