404 HOW CROPS GROW. 



which occur in the soluble crystalloids of aleurone 

 (p. 105) and haemoglobin (p. 97) are highly diffusible, 

 as certainly is the case with the peptones. 



Gaseous bodies, especially the carbonic acid and oxy- 

 gen of the atmosphere, which have free access to the 

 intercellular cavities of the foliage, and which are for the 

 most part the only contents of the larger ducts, may bo 

 distributed throughout the plant by osmose after having 

 been dissolved in the sap or otherwise absorbed by the 

 cell-contents. 



Influence of the Membranes. The sharp separa- 

 tion of unlike juices and soluble matters in the plant 

 indicates the existence of a remarkable variety and range 

 of adhesive attractions. In orange-colored flowers we 

 see upon microscopic examination that this tint is pro- 

 duced by the united effect of yellow and red pigments 

 which are contained in the cells of the petals. One cell 

 is filled with yellow pigment, and the adjoining one with 

 red, but these two colors are never contained in the 

 same cell. In fruits we have coloring matters of great 

 tinctorial power and freely soluble in water, but they 

 never forsake the cells where they appear, never wander 

 into the contiguous parts of the plant. In the stems 

 and leaves of the dandelion, lettuce, and many other 

 plants, a white, milky, and bitter juice is contained, but 

 it is strictly confined to certain special channels and 

 never visibly passes beyond them. The loosely disposed 

 cells of the interior of leaves contain grains of chloro- 

 phyl, but this substance does not appear in the epidermal 

 cells, those of the stomata excepted. Sachs found that 

 solution of indigo quickly entered the roots of a seedling 

 bean, but required a considerable time to penetrate the 

 stem. Hallier, in his experiments on the absorption of 

 colored liquids by plants, noticed, in all cases when 

 leaves or green stems were immersed in solution of indigo, 

 or black-cherry juice, that these dyes readily passed into 



