516 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 2 



anthocyan, which is precipitated by caffein, giving a loose 

 compound of tannin and caffein, called a "my elm-formation." 

 Ammonia also gives this precipitate even in a solution as dilute 

 as 1-15,000. Czapek investigated the effect produced by the 

 application of a great variety of organic compounds and some 

 inorganic acids in varying dilutions and for different periods 

 of time, and determined the concentration at which exosmosis 

 just occurred, i. e., the critical point. At the higher concen- 

 trations exosmosis of the tannoid substance readily occurred, 

 as shown by the absence of the "ravelin-formation" when 

 caffein or ammonia was subsequently added. At the lower 

 concentrations exosmosis did not occur and a precipitate was 

 obtained, while at the critical point the precipitate was barely 

 visible and usually in the form of fine particles. 



By the use of his "capillar-manometer," Czapek was able 

 to measure the surface tension exerted by the various concen- 

 trations, and found that, considering the surface tension of 

 water as unity, that of the critical concentrations was approx- 

 imately .68 in most cases. This lowering of the surface ten- 

 sion he considered as essentially a physical phenomenon which 

 is intimately connected with the osmotic activities of the 

 plasma membrane and is to be differentiated from the toxic 

 action of injurious substances, e. g., anesthetics, whose action 

 is chemical in large part, since even in very dilute solutions 

 these caused marked exosmosis. Czapek used both aqueous 

 and colloidal solutions and found that in general the critical 

 concentrations had a surface tension of .68 in terms of water 

 as unity. Inversely, he therefore concluded that the surface 

 tension of the plasma membrane was also approximately .68 

 for the plant cells investigated. In his study of acids he found 

 results coincident with those of Kahlenberg and True ('96) 

 in that N/6400 was the critical concentration for exosmosis 

 of the tannin bodies, just as those workers had found it to be 

 the critical concentration for growth of Lupinus seedlings in 

 solution culture. 



In his later experimental work Lepeschkin ('11) obtained 

 additional evidence tending to confirm and add to his previous 

 results, as mentioned above. Thus he found that aniline dyes 



