134 Hydration and Growth. 



series was swelled at the temperature of 30° to 31° C, at which the 

 shoot had stood for several days. The second series was swelled at 

 17° to 19° C, in which equivalent shoots stood, which were to be 

 used as a comparison.^ 



The most remarkable feature of these measurements is that in 

 which the material grown at 30° to 31° C. for two days showed a greater 

 increase when swelled at a lower temperature (see p. 119). The entire 

 set of reactions is indicative of a colloidal complex of different con- 

 stitution from that of green plants. 



Analyses necessary to establish the nature of such divergent con- 

 stitution of etiolated opuntias could not be made, but data obtained 

 from other species grown in darkness are available. The results of 

 Palladin show that stems of such plants have less nitrogen than nor- 

 mal green plants, and all workers who have dealt with this subject 

 agree that the ash-content of etiolated organs is relatively greater than 

 in green stems.^ 



There is not general agreement as to the distribution of nitrogen in 

 etiolated plants, but there seems to be imanimity in the conclusion 

 that the total nitrogen-content is less than in normal plants. Accord- 

 ing to Karsten, all parts of the plant have less sugar and "gums" when 

 grown in darkness.* As the gums include the pentosans, which with the 

 nitrogenous compounds make up the hydration machine, it is to be 

 seen that the etiolated plant presents the features of lessened protein, 

 decreased pentosans, and increased salts, all of which would tend to a 

 lessened imbibition capacity in both fresh and dried material. How 

 much the lessened nitrogen-content would contribute to this general 

 decrease might only be known by a determination of the character of 

 the compounds in the two instances. 



All of the facts concerning imbibition by hving plants and by bio- 

 colloids tend to show that the proposal of Palladin to ascribe the vari- 

 ous departures of growth in plants in darkness to transpiration effects 

 is not tenable. There is much foundation for the belief that form may 

 be largely affected by the water-relation, but with respect chiefly to 

 imbibition capacity, as a resultant of the protein-pentosan-salt com- 

 plex with varying acidity. It would seem, therefore, that for Palladin's 

 contention that the ash constituents of the etiolated plant exercise a de- 

 termining effect on the growth and development in darkness by in- 

 fluencing transpiration, we may safely substitute an assertion that 

 the important effect of the salts is that which they have on the imbibi- 



'MacDougal. The influence of etiolation upon chemical composition, in "The influence of 

 light and darkness upon growth and development." Mem. N. Y. Bot. Garden, 2: 300-305. 

 1891. 



' Palladin, W. Eiweissgehalt der grQnen und der etiolirter Blatter. Ber. d. deut. bot. Ges., 

 9: 191. 1903. 



' Karsten, H. Die Einwirkung des Idchtes auf das Wachstums der Pflanzen. Jena. 1870. 



