CAUSES OF THE MOTION OF JUICES. 563 
come more diffusible in some of their combinations. 
Schumacher asserts that carbonates and phosphates of the 
alkalies considerably increase the osmose of albumin 
through membranes of nitrocellulose, (Physik der Pflaxnze, 
-p. 128.) It is probable that those combinations o1 modi: 
fications of the albuminoids which occur in the soluble 
erystalloids of aleurone (p. 105,) and haemoglobin (p. 97,) 
are highly diffusible. The fact of their having the form 
of crystals is of itself presumptive evidence of this view, 
which deséxves 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 
part the only contents of tne 1arger 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 effect of yellow and red pigments which are con- 
tained 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 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, 
