350 MACDOUGAL AND SPOEHR— GROWTH AND IMBIBITION. 



enous matter necessary to cause an agar mixture to behave in this 

 manner were made. Ordinary agar contains some nitrogen and 

 salts/" and it is possible that the varying amounts might cause some 

 disagreement of results obtained by the use of different lots of this 

 substance. 



The series of experimental trials with colloids which might dis- 

 play some of the fundamental physical properties of protoplasm of 

 plants has resulted in finding that a mixture of substances of two 

 of the three more important groups of constituents, carbohydrates 

 and proteins, shows the imbibitional behavior of tissues and tracts 

 of protoplasts of the plant. The differential action of such colloidal 

 masses in distilled water, acid and alkaline solutions yields many 

 striking parallels with growth. The changes from acidity to alka- 

 linity have, so far as this type of experiment has been repeated, been 

 made abruptly to avoid instrumental errors. Some acid or some 

 alkali remained in the dishes when the change was made, and a cer- 

 tain amount of acid or alkali fixed or absorbed in the colloidal sec- 



FiG. 13. Auxographic tracing of changes in length of shoot of Opuntia 

 showing elongation and shortening (for comparison with Fig. 12). 



tion, and neutralization, acidification or the reverse took place slowly 

 with some formation of salts as might likewise occur in the plant 

 (see Fig. 13). 



It is through the relations indicated that metabolism or respira- 

 tion may affect growth by the modification of imbibition capacity. 

 Thus the accumulating surplus of acid in Opxintia begins to lessen 

 by disintegration at daybreak and the decrease continues until about 



1^ See Noyes, H. A., " Agar for Bacteriological Use," Science, Vol. 44, 

 No. 1 144, p. 797, 196. 



