1917] AGRICULTURAL BOTANY. 129 



not claimed that the nontranslocation of iron is a general rule, but the authors' 

 observations on rice and pineapples indicate that iron, after once being trans- 

 ported to the leaves, becomes immobile. 



The poisonous influence of lithium salts on plants, H. Frebking {Flora 

 [Jena], n. scr., 8 {1915), No. 4, pp. U9-453).— It is stated that lithium, like 

 magnesium, is poisonous to organisms requiring calcium, but not to calcium- 

 free algae and fungi. The poisonous influence of lithium is more pronounced 

 than that of magnesium. While the influence of magnesium can be annulled 

 by the employment of calcium salts, that of lithium is only retarded in this way. 



The orientation of primary terrestrial roots with particular reference to 

 the medium in which they are grown, R. M. Holman {Amer. Jour. Bot., S 

 {1916), No. 6, pp. 274-318, figs. 7). — An account is given of a study, principally 

 as relating to the vetch, lupine, and pea, which gave concordant results as re- 

 gards the behavior of the root tip in relation to the media employed. 



It is stated that differences in the amount of water in the media did not 

 affect the behavior of the roots in this regard. Changes of geotonus due to 

 their stay in air were not shown to affect root direction. The failure of the 

 roots in air to reach the vertical appears to be due to the absence of mechanical 

 resistance to the advance of the root tip in this medium. Secondary curvature 

 of the roots in earth, sand, sawdust, sphagnum, or other such media, is com- 

 plete, because resistance in these media causes passive depression of the root 

 and prevents complete flattening of the tip curvature. Thigmotropism is not 

 a factor in the difference in the behavior of roots in air and in earth or other 

 nonfluid media. Resistance in the medium influences not only secondary but 

 primary curvature, that is, curvature directly following the placing of the root 

 in a position of stimulation. 



The thermometric movements of tree branches at freezing temperatures, 

 C. C. Trowbridge {Bui. Torrcy Bot. Club, 43 {1916), No. 1, pp. 29-66, figi. 19).— 

 Summarizing observations which are considered to have made some advance in 

 the study of the influence of temperature on branch movement, the author 

 states that depression of the branches of Tilia europwa begins at or just above 

 32° F. and continues at least as far as 0°, the lovrest point at which observations 

 were made. The atmospheric humidity has a negligible influence in this re- 

 spect. Below 32° there is a stiffening of the branch, offering resistance to the 

 depression. The width of longitudinal frost cracks, after they become estab- 

 lished, corresponds somewhat to the temperature below 32°. There are indica- 

 tions that the bending is closely related to the process that produces the frost 

 cracks. 



Platanus orie7italis and Paulotniia tomentosa show scarcely a trace of the 

 thermometric movement exhibited by the linden. 



The mechanism, of movement and the duration of the effect of stimula- 

 tion in the leaves of Dionaea, W. H. Brown {Amer. Jour. Bot., 3 {1916), No. 2, 

 pp. 68-90, fig. 1). — It is stated that leaf closure in Dionsea is due largely to an 

 increase on the ventral or convex side of the leaf in cell size, corresponding to 

 a stretching of the cell walls which is soon rendered permanent by growth, and 

 that leaf opening is due to the slow enlargement, likewise corresponding to 

 growth, of cells on the dorsal or concave surface. Stimulation of the leaf 

 is followed by a great acceleration of growth, and apparently immedi- 

 ately by a decrease in osmotic pressure of the dorsal cells resulting in the 

 passage of water from these to those of the ventral region. Starch is de- 

 posited abundantly in the dorsal cells soon after closure occurs. Leaves killed 

 in boiling water just after closure open again if transferred through alcohol 

 to xylene and close again when returned to water. 



