348 MacDOUGAL— HYDRATION AND GROWTH. 



The living matter of the plant cell includes pentosans which are 

 to be taken as weak acids and which show only slight dissociation, 

 and of albumins or amino-compounds, w'hich undergo a greater 

 hydration with increasing concentration of hydrogen ions. Hydra- 

 tion of the carbohydrate or pentosan constituent or protoplasm is 

 affected in the reverse manner. The actiial rate of growth of any 

 protoplast would therefore be a resultant of the opposing action of 

 pentosans and of albumins. 



Swelling, hydration or growth of bio-colloidal masses is not 

 however simply a matter of hydrogen ion concentration, as we have 

 found that the hydration and swelling of pentosan-protein colloids 

 simulating protoplasm, of tissues of living plants and of dried cell- 

 masses, is facilitated by the amino-compounds which dissociate as 

 bases. The greatest increases occur in concentrations of o.oi M to 

 o.ooi M of such substances as alanin, asparagine, glycocoll, phenyl- 

 alanin, and ethylamine. Concurrent accelerations of grow'th result- 

 ing in increased dry weight and greater volume are reported by 

 many experimenters using such substances in culture solutions. It 

 is highly probable that bases (cations) may have some effect on 

 hydration or growth, a matter yet to be tested.^ 



The essential feature of an idealized growth is the accretion or 

 addition of water and material to the mass of colloid constituting the 

 cell. The actual mechanism of incorporation is not easily delineated. 

 If protoplasm consisted of a system of colloidal structures such as 

 those of the pentosans and the proteins interwoven, but not diffusing 

 into each other, the more solid material which lowers the surface 

 tension to the greatest extent, having the least attraction for water- 

 molecules, would tend to usurp the position of the surface layer. 

 Furthermore, the solid phase, whether it be in the form of globules 

 or in the continuous element, would tend to increase and crowd to- 

 gether with a lessening of the more liquid phase. This would imply 

 that when gelatine in small proportion is mixed with agar or starch 

 paste in the larger proportion that the carbohydrate would form 

 both the colloidal framework or mesh, as well as the external layer 



1 See MacDougal and Spoehr, " The Effect of Organic Acids and tlieir 

 Amino-Compounds on the Hydration of Agar and on a Biocolloid," Proc. 

 Soc. Expcr. Biol, and Med., i6: 2)2)' ipiS- 



