DEPARTMENT OF BOTANICAL RESEARCH. 51 



15. In Zea mays the geotropic response of the roots appears to be 

 much weaker in a soil-atmosphere containing 2 per cent oxygen than 

 in normal air. 



16. The first observable morphological effect of poor aeration in 

 Pisum sativum is a shrinking of the meristematic tissue of the root- 

 tip. If this alteration proceeds beyond a certain stage, recovery 

 upon the admission of air does not take place; if, however, the reaction 

 has not progressed far, recovery is possible. In the last event the 

 effects of the reaction to a condition of poor aeration may persist for a 

 period as a constriction of the growing root. 



The Action of Vitamins, Amino-Co7npounds, and Salts on Hydration, 

 by D. T. MacDougal. 



The assertion was made in an earlier report that the salts of the com- 

 mon metals which enter into nutritive solutions, as potassium, mag- 

 nesium, sodium, and calcium, might find their chief importance in 

 restricting, limiting, or defining hydration. Such an action is exerted 

 by these bases in the form of hydroxides when tested at O.OOIn. 

 MacDougal and Spoehr found later that the hydroxides of the strong 

 metallic bases limit the hydration of agar according to their position 

 in the electromotive series, the least swelling taking place under the 

 action of the strongest base at concentrations of 0.01 n, with the ap- 

 parent exception of rubidium. Beginning with the strongest, the 

 series runs K, (Rb), Na, Li. The various effects of barium, calcium, 

 and strontium are not so clearly determined, and the quantitati\'e 

 relations of these metals are not known definitely. Hydration values 

 of agar at O.OIn were Sr (OH)o = 815, Ca(OH)2 = 860, Ba(OH)2 = 000. 

 These concentrations are far beyond the actual range of condi- 

 tions in the cell, however, and when reduced concentrations were 

 used it was seen that the hydration of agar in calcium hydroxide ex- 

 ceeds that in water at O.OOOIn of the hydroxide, and this effect is 

 also produced at O.OOOOIn. There was increase of hydration beyond 

 that of water by dilute solutions of hydroxides of calcium, potassium, 

 rubidium, sodium, and lithium, and excess values for aniline and am- 

 monium hydroxides were obtained. It was also seen that the strongest 

 of the bases, potassium, in the form of hydroxide would increase the 

 swelling of agar-albumin mixtures to a point beyond that taking place 

 in water alone. 



The next logical step was to test the effects of salts of the common 

 metals on swelling of the biocolloidal components. Here again the in- 

 teresting fact was found that as chlorides sodium and potassium at 

 O.OOIm caused greater hydration of agar than water, the swelling being 

 greater in the potassium. At O.OOOIm, sodium, potassium, magnesium, 

 and calcium chlorides caused greater swelling than in water, the maxi- 

 mum swelling being in sodium, the next in potassium, and the least in 

 calcium. 



