1917] AGRICULTURAL BOTANY. 525 



plants having a greater capacity for water when slightly alkaline. Water 

 capacity of cacti increases with the dry weight up to the age of one year or 

 more (maturity), then decreases. Gelatin with a little agar makes a mixture 

 displaying imbibition comparable to tlmt of plants. Imbibition capacity (which 

 is less at night than in the daytime) influences transpiration and movements. 

 Studies were made on the relative influences of imbibition and turgor in the 

 growth of pollen tubes in cane sugar, acids, and alkalies. The contained 

 colloids swell more in acid than in alkali of low concentrations. 



The ratio of precipitation to evaporation is the factor which limits the 

 areas of forest, grassland, and desert. A new subdivision of vegetational areas 

 has been worked out, as well as a new method of determination of the domina- 

 tion of different growth forms. 



Flattened plant bodies meridionally placed receive more heat than those set 

 at right angles to this position, attaining temperatures of 53° C. (127.4° F.) 

 or more and transpiration and dry weight corresponding to the exposure. 

 Hoots of different plants show varied relations to oxygen, which is corre- 

 lated with soil penetration and habit, and similar differences appear as regards 

 the temperature conditioning growth. The forms taken by root systems are 

 greatly affected by environment. Roots of Salix will grow for some time 

 without oxygen. 



Extensive study has been made of the concentrations of the sap of plants in 

 mountain and desert habitats. Sap of parasites is usually, but not always or 

 necessarily, of higher concentration than that of their hosts. 



Wide divergences appear in the progenies of single species of CEnothera from 

 widely separated localities, and striking aberrants or mutants were noted. The 

 revegetation of an island has been followed since 1908, wlien there were two 

 individuals present, to 1916, when there were 470 individuals, representing 10 

 species. 



Variations in climate as related to vegetation in earlier geological periods 

 are attributed chiefly to the frequency and distribution of cyclonic storms. The 

 study of the Mohave River yields evidence which is of value in making out the 

 evolutionary history of the vegetation in this ancient desert. The underflow 

 being of great importance to vegetation, it has been found that artesian condi- 

 tions would not necessarily require a bowl-shaped basin, and some generali- 

 zations of practical value have been obtained. 



Osmotic pressure in roots and in leaves in relation to habitat moisture, 

 V. Iljin, p. Nazaeova, and M. Ostrovskaja {Jour. Ecology, 4 {1916), No. 3-^, 

 pp. 160-173). — The authors have made a study of the vegetation (represented 

 by various genera and species) of three types, swamp, meadow, and grass 

 steppe, in the Valuyki district, in the Government of Voronezh. It is stated 

 that the influence of differences in water supply can be noted in leaf and root. 

 The osmotic pressure shows variations due to external influences as well as to 

 internal structure. A close relation is always observable between intensity of 

 osmotic pressure and the amount of water at the disposal of the plant cell. 



Nitrogen compounds in mulberry leaves, E. Katayama {Bui. Imp. Sericult. 

 Expt. Sta. Japan, 1 {1916), No. 1, pp. 1-30). — The author reports on a study of 

 the various nitrogen compounds and their percentages present in mulberry 

 leaves, with some reference to their utilization by silkworms in their nutritive 

 processes and in the manufacture of their products. 



The emergence of the aerial organs in woodland plants, E. J. Salisbuby 

 {Jour. Ecology, k {1916), No. S-4, pp. 121-128, figs. 7).— A study has been made 

 of the three principal types of adaptation to overcome the resistances to emer- 

 gence from the soil by various plants on germination. 



