CAUSES OF THE MOTION OF JUICES. 365 



come more diffusible in- some of their combinations. 

 Schuraacher asserts tliat carbonates and pliosphates of the 

 alkalies considerably increase the osmose of albumin 

 through membranes of nitrocellulose, {Physilc der Pflanze, 

 p. 128.) It is probable that those combinations or modi- 

 fications of the albuminoids which occur in the soluble 

 crystalloids of aleurone (p. 105,) and haemoglobin (p. 97,) 

 are liighly diffusible. The fact of their having the form 

 of crystals is of itself presumptive evidence of this view, 

 Avhich deserves to be tested by experiment. 



Gaseous bodies, especially the carbonic acid and oxygen 

 of the atmosphere, -which have free access to the intercel- 

 lular cavities of the foliage, and which are for the most 

 fiart the only contents of the larger ducts, may be dis- 

 tributed 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 separation 



of unlike juices and soluble matters in the plant indicates 

 the existence of a remarkable variety and range of ad- 

 hesive attractions. In orange-colored flowers we see upon 

 microscopic examination that this tint is produced by the 

 united efiect of yellow and red pigments which are con- 

 tained in the cells of the j)etals. 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 tinc- 

 torial 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 chlorophyll, 

 but this substance does not appear in the epidermal cells, 

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