SYMPOSIUM ON COLLOIDS 59 



and with liquid water when it contains about 1 100 per cent. 

 If gelatin fully imbibed in a saturated atmosphere, is placed 

 in water a rapid absorption occurs and the liquid water equili- 

 brium is finally approximately reached. The reverse process 

 takes place when a gel fully imbibed in liquid water is placed 

 in a saturated atmosphere. Filter paper absorbs about equal 

 amounts from saturated atmosphere and water. This char- 

 acter of gelatin and other gels is not certainly explained phys- 

 ically, but that does not concern the biologist so much as the 

 question of whether the living body behaves similarly. Martin 

 (24 and unpublished work) has found an exact counterpart of 

 this behavior of gels in the pollen of alfalfa. The pollen has 

 a very narrow range of water supply necessary for its germ- 

 ination. This is the main factor in the uncertainty of seed 

 production — a matter of considerable economic significance in 

 the United States. In distilled water the grains swell rapidly 

 and burst. In a saturated atmosphere they germinate rather 

 abundantly ; but will not germinate in an atmosphere appreci- 

 ably below the point of saturation. A number of experiments 

 indicate that the final water equilibrium is an important factor 

 here, although the rate of water absorption is likely of some 

 significance. Shull (unpublished work) has found for several 

 sorts of seeds that they contain much more water when in 

 equilibrium with distilled water than when in equilibrium with 

 saturated atmosphere. 



If the entire plant acts like a piece of gelatin it should 

 transpire to a saturated atmosphere when its lower end is in 

 water. Dixon (25) claims that this occurs. This character 

 of gels may be acting along with raised temperature due to 

 absorption of radiant energy in maintaining transportation in 

 plants of tropical rainy regions. It is a common thing in plant 

 physiology to grow what are naturally soil or water roots in a 

 saturated atmosphere and assume that they are in a normal 

 condition. Aside from the rate of water absorption we have 

 this character of gels raising a question as to the amount cap- 

 able of being absorbed. Every worker in plant physiology has 

 observed peculiar characters in roots grown in saturated atmos- 

 phere, such as reduced rate of elongation and profusion of root 

 hairs. This gel character of plants may also play a part in 

 guttation. 



V DIFFUSION IN A COLLOIDAL MEDIUM 



Peculiar diffusion and precipitation phenomena occur in col- 

 loidal substrata. Kiister (26) attempts to relate these causally 

 with the most diverse features of plant anatomy. His point of 



