224 EXPERIMENT STATION EECOED. 



It is stated that roots of L. albus are always positively hydrotropic, the reac- 

 tions occurring only within a relative humidity of 80 to 100 per cent, the mini- 

 mum effective moisture difference at 20° C. being a fall of 0.2 per cent, the 

 optimum 0.4 per cent, and the maximum 0.5 per cent. 



A presentation period was not determined, but reaction becomes perceptible 

 in six hours. The hydrotropic sensitivity resides chiefly in the tip, but also in 

 lesser degree in the parts above. 



Of the two factors, one mechanical and the other vital, which are held to 

 determine the reaction of the root to a hydrotropic stimulus, the intensity varies 

 inversely as the former and directly as the latter; the latter predominating 

 under weak, the former under intense stimulus. 



Hydrotropism is not regarded as a special case of traumatropism, but as prob- 

 ably equivalent to osraotropism. 



A bibliography is given. 



The exchange of ions between the roots of Luplnus albus and culture solu- 

 tions containing one nutrient salt, R. H. Tul-e and H. H. Baktlett {Amcr. 

 Jour. Bot., 2 (1015), No. 6, pp. 250-218, figs. 13). — In continuation of work by 

 one or both of these authors as previously noted (E. S. R., 26, p. 624 ; 31, p. 730; 

 32, p. 824), the authors report that, in recent studies with seedlings of white 

 lupine, roots grown in darkness in distilled water gave up their salts to the 

 water at a varying rate until the plants died from exhaustion of their reserves. 



Monobasic potassium phosphate and potassium chlorid solutions act e.-^sen- 

 tially like distilled water in the concentrations herein employetl. Solutions of 

 potassium sulphate and potassium nitrate differ from the above only in a slight 

 absorption phase re.sulting in a minimal net gain in salts to the plant. Absorp- 

 tion and gi-owth in the sodium chlorid occur essentially as in potassium nitrate 

 and potassium sulphate. 



Solutions of magnesium nitrate, also those of magnesium sulphate, show a 

 slight but distinct absorption phase resulting in a net gain in salts to the plant. 

 Higher concentrations result in action toxic to the plants, lower in a leakage 

 therefrom. 



Calcium nitrate and calcium sulphate were actively absorbed by the roots in 

 all concentrations studietl, and apparently enable the plants to retain possession 

 of the salts already present in the plant. 



The exchange of ions between the roots of Lupinus albus and culture solu- 

 tions containing two nutrient salts, R. II. True and H. H. Babtlett (Amcr. 

 Jour. Bot., 2 (1915), No. 7, pp. 311-S23, figs. 3). — In this investigation seedlings 

 of L. albus were supplied with solutions containing mixtures of the nitrates of 

 calcium, magnesium, and potassium in pairs in different proportions and in dif- 

 ferent total concentrations. 



It is stated that when these nitrates are offered in pairs in solutions varying 

 from 120 NXIO— ' to 480 NXIO— ', the roots usually absorb more electrolytes 

 than from the solutions tested singly. In mixtures, as in single solutions, ab- 

 sorption tends to increase when concentration is Increased, the magesium salts 

 appearing to offer an exception on account of the narrow range of physiologi- 

 cally useful concentrations of this ion. 



In mixtures of the nitrates of calcium and potassium, the unfavorable effect of 

 the latter ion is seen in the large proportion of the former required to give maxi- 

 mum absorption, though the value of a small amount of potassium ion is evi- 

 dent. The absolute amount of calcium seems to be of great influence, a largo 

 proportion thereof increasing absorption in the greater dilutions. The favor- 

 able influence of this ion is therefore striking in mixed as well as in unmixed 

 solutions. 



