DEPARTMENT OF BOTANICAL RESEARCH. 57 



and renewed at intervals of 12 and 24 hours. Such renewals were 

 attended by accelerations in the rate and increases in the total swell- 

 ing. Agar and biocolloids of agar and gelatine showed this action in a 

 marked manner. Sections of equal parts of these two components 

 exhibited reactions in which the exaggerated swelling resulting from 

 renewals were partly retracted very slowly on the third day. After 

 this the exaggeration slowly decreased and the retraction increased 

 until the two balanced about the eighth day. The two movements 

 continued for a total period of 67 days. It is suggested that the 

 exaggerated swelling following a renewal of the solutions may be due 

 to the formation of glycocoU agarate, the bulk of which might be 

 greater than that of the agar. Diffusion of this material from the 

 section would result in a retraction or shrinkage. 



10. Plates of colloids cast on glass and prevented from shrinking in 

 area take on a heterotropic structure which varies in agar, gelatine, 

 and in mixtures of the two. The swelling of an agar plate is almost 

 wholly in thickness, so that the increase of a hydrated section is 

 denoted directly by the thickness reached. Gelatine plates prepared 

 in the same manner may increase as much as 60 per cent in length and 

 width while swelling. Plates of mixtures of the two swell from 6 to 16 

 per cent in length and width, this amount being modified by the 

 character of the hydrating solution. These effects, which may play 

 an important part in morphological procedure in the cell, seem to 

 indicate a meshwork structure of biocolloids, as it does not seem 

 possible for emulsions to be differentiated in the manner implied. 



Swelling of Agar in Solutions of Amiiio-Acids and Related Compounds, by 

 D. T. MacDougal and H. A. Spoehr. 



The protoplasmic bodies of the cells of plants are composed chiefly 

 of pentosans or mucilages and proteins, with an undetermined amount 

 of lipins, while the common bases, potassium and sodium, are prob- 

 ably present in the form of salts of organic and inorganic acids. 



The hydration or capacity of the pentosans to absorb water is such 

 that their action doubtless plays a major role in growth and other 

 variations in volume. Detailed study of agar as representative of 

 these pentosans or mucilages shows that there are very few such solu- 

 tions in which agar swells to a greater degree than it does in distilled 

 water. Some substances, however, increase the hydration of agar 

 above that attained in pure water; these are the amino-acids. The 

 amino-compounds are of such immediate biological importance that a 

 discussion of their action deserves special consideration, and may aid 

 in explaining the scattered results obtained by various workers in 

 which increased total growth and apparently catalytically accelerated 

 actions have been obtained by the addition of certain amino-acids to 

 culture solutions. 



