SYMPOSIUM ON COLLOIDS 



:3 



for oil droplets and starch grains she speaks of the lipoid pig- 

 ment phase as distributed through the hydroid protein phase 

 to amicronic dimensions. This distribution is easily deformed 

 by various reagents giving all types of structure formerly 

 claimed for the organ. Excessive water absorption caused by 

 opening the cells and bringing the chloroplasts directly into 

 contact with water or even by long soaking of the entire leaf, 

 produces a variety of deformations. As shown by staining re- 

 actions, water never produces a complete separation of the two 

 phases. Such altered structures appear frequently in nature and 

 they probably result from peculiar water relations of the 

 plastid. Surface tension active substances as well as other 

 fixing and killing agents in sufficient concentration cause a 

 complete separation of the two phases. This emphasizes the 

 great danger of concluding as to the structure of a living cell 

 from fixed and stained material. (See also citation 4). 



Other evidence is offered for the colloidal state of chloro- 

 phyll in the living plastid. It has been known for a long time 

 that chlorophyll in an alcohol solution is readily decomposed 

 by sunlight. This has called for an explanation of the ap- 

 parent or real light stability of chlorophyll in the illuminated 

 leaf. Wiesner believed that protective action of fatty bodies 

 and continual synthesis account for the maintained amount, 

 while Reinke suggested that chlorophyll forms a light stable 

 compound with proteins of the plastid. Iwanowski (10) ac- 

 cepts neither of these views, but thinks the light stability of 

 chlorophyll is explained on the basis of the colloidal condition 

 in the plastid. He found chlorophyll extract in 49 per cent 

 alcohol far more light resistant than that in 95 per cent alco- 

 hol. In the former case it is in colloidal solution, in the latter 

 molecular. He also shows that as the colloidal concentration 

 of the solution increases and the degree of dispersion corrc 

 spondingly decreasess light stability rises. Finally in the con- 

 centration and degree of dispersion probably existing in the 

 chloroplast, it is light stable. While the Iwanowski conception 

 has evidence in its favor there is also no important evidence 

 against the Reinke view. Iwanowski also finds evidence for 

 carotin and xanthophyll of the plastid protecting the chloro- 

 phyll against light destruction. Herlitzka (11), using care- 

 fully purified chlorophyll, finds that it shows little if any 

 fluorescence in collodial solution, while this property is very 

 evident in a molecular solution. The lack of marked fluor- 

 escence in the plastid is probably due to the colloidal state of the 

 pigment as well as to the turbidity of the plastid, formerly 

 offered as the explanation. 



