AGRICULTURAL BOTANY. 527 



izing effect beiiiif greatest in the case of luagneslum sulphate and least in that 

 of sodium carbonate. As a rule the more sensitive the species to the pure solu- 

 tion, the greater was the counteracting effect of the calcium salt. 



Amounts of calcium sulphate smaller than that necessary to saturate the 

 mixed solution showed a marked neutralizing effect upon the more toxic salt, 

 but the minimum amount of calcium sulphate capable of producing such effect 

 remains to be determined. For the white lupine the presence of 0.5 gm. of 

 calcium sulphate was found as effective as seven times that amount in neu- 

 tralizing sodium chlorid, while for sorghum 0.1 gm. was as effective as twenty 

 times that amount. To secure the most effective possible neutralization of 

 sodium chlorid five times as much calcium sulphate was required in the case of 

 the white lupine as in that of the sorghum, although the limits for these two 

 plants were approximately the same both in pure sodium chlorid and in sodium 

 chlorid with an excess of calcium sulphate. 



While it was found impossible to compare the i*esistance of the different 

 plants to ]>ure solutions of the single salts with that of the same species in dif- 

 ferent combinations of alliali salts occurring in western soils, their behavior in 

 mixed solutions sho^A•ed a close approximation to that observed under natural 

 conditions. 



The soil preferences of alpine and subalpine plants, M. L. Fernald (RIio- 

 flora. .0 (1907), .Vo. 10.1, pp. I'lH^m.i). — The results are given of a prolonged 

 study of several hundred species of alpine and subalpine plants to ascertain 

 the factors determining their distribution. The author claims that precipita- 

 tion, exposure, fineness of soil particles, and water content of soils are of sec- 

 ondary importance in determining the presence of certain species of plants. 

 The controlling factor is held to be the chemical nature of the soil, and striking 

 coincidences are noted between the soil-forming rocks of mountains and cliffs 

 and the distribution <tf the plants which cover them. In the regions studied 

 it was found that the distribution of plants is largely controlled by the prepon- 

 derance in the soil of potassium, calcium, and magnesium, although it was 

 found in certain areas that soda, iron, and other elements were of equal im- 

 portance in determining the range of plants. 



The production of deleterious excretions by roots, O. Schreiner and H. S. 

 Heed {Hid. Tonctj Bot. CJuh, 3', il'Ml), Xo. 6, pp. 279-303, fig. 7 ) .—Seedlings 

 [ of wheat, oats, maize, and cowpeas were grown in agar in specially constructed 

 tubes placed in glass vials attached to a clinostat. The roots developed in the 

 agar and gave indications of chemotropism, which was attributed to deleterious 

 substances excreted by the roots. 



The authors, summarizing the results of their investigation, state that their 

 experiments show that healthy growing plants excrete from their roots sub- 

 stances which have a deleterious effect upon the' growth of the root. The 

 excreta produced by the roots are so small in amount as not to be detected by 

 chemical analysis, but the chemotropic sensitiveness of the plant demonstrates 

 experimentally the presence of root excreta. 



It was found as a rule that the excreta produced by a given plant are more 

 toxic to plants of that same species than to others, and, so far as studied, are 

 more toxic to closely related species than to those more distantly related. 



The production of toxic excretions by the roots of the higher plants, it is 

 held, ai)pears to afford an explanation of some of the important i)henomena 

 coimected with association, invasion, and succession of plants. 



The galvanotropism of roots, Jessie S. Bayliss {Ann. Bot. [London]. 21 

 {1907), No. S3, pp. 387-'iO'}, flijs. //, dgms. 2). — This is an account of experiments 

 with seedlings of beans, maize, peas, sunflowers, pumpkins, and castor beans, 

 in which the effect of a galvanic current upon the roots was tested. 



