128 EXPERIMENT STATION EECOKD. [Vol. 37 



apple. Observations on other trees are also noted. No evidence was obtaine<l 

 to show that the formation of phloem continued later than that of xylem. 



The epidermal cells of roots, Edith A. Roberts {Bot. Gaz., 62 {1916). No. 

 6, pp. 488-506. figs. 17). — This attempt to determine the varying factors within 

 and without the epidermal cell of the root and their reciprocal relations was 

 prompted by the fact that frequently the pre.sence or the absence of root hairs 

 is used as an indicator of clianged external conditions. 



It is stated, as the re.sult of study with various plants, that the formation of 

 a root hair is first indicated by the swelling of the outer wall of the epidermal 

 cell. This is due to the fact that the physical resistance of the wall is over- 

 come by the osmotic pressure within the wall, continued swelling and growth 

 occurring in a region of comparatively slight resistance which has no apparent 

 relation to the po.'jition of the nucleus. The wall of the root hair is composed 

 of an inner cellulose membrane and an outer membrane of calcium pectate, soil 

 particles being held to the layer by pectin mucilage, these facts accounting 

 supposedly for the high absorbing efficiency of the root hairs. 



New determinations of permeability, S. C. Bkooks (Proc. Nat. Acad. Set., 

 2 {1916), No. 10, pp. .'j69-57Jf. figs. 6). — The author reports determinations of 

 permeability of plant tissues by a new method claimed to be independent of 

 methods or improvements thereof, as previously employeil. The results are 

 said to agree in showing that living protoplasm is normally permeable to the 

 salts employed, but that salts in solution may alter permeability. Some (as 

 sodium chlorid) cause an increase, others (chlorlds of calcium, lanthanum, 

 and cerium) a decrease followed by an increase, the permeability remaining 

 normal in a balanced solution. 



Studies on exosmosis, S. C. Brooks {Auier. Jour. Bat., 3 {1916), No. 9. pp. 

 J/S3-Ji92. figs. -'/). — The author has made a study on the tendency of osmotically 

 active substances to diffuse out of the cell in the course of experiments where 

 turgidity or osmotic pressure is used as a criterion of permeability. Strips 

 from scapes of dandelion were used in experiments in which the exosmosis of 

 electrolytes into distilled water from such strips was determined after their 

 treatment with distilled water or solutions of the chlorlds of sodium, calcium, 

 or cerium. 



It was found that sodium salts increase, while calcium salts decrease, the 

 rate of exosmosis of other electrolytes from the protoplasm of Taraxacum 

 officinale. It is possible to prepare a soluti<m such that, when it is used at a 

 concentration isotonic with the protoplasm. It causes no perceptible alteration in 

 the permeability of the plasma membrane. 



The role of osmotic pressure of a soil solution in the culture of wheat, 

 N. M. Tui.AiKov (TouLAiKOFF) {Zhur. Opi/tn. Agron. {.Jour. .Agr. Exp!.), 17 

 {1916), No. 2, pp. 122-164. figs. 9). — The osmotic pressure of the soil solution 

 is considered of great importance in the development of wheat, manifesting 

 itself at germination and at every other Important period in the life of the 

 plant. Some particulars are given regarding ob.served modifications of the 

 relations between the grain and the stalk produced. These may be made to 

 deviate considerably from the normal or observed tendency In the direction 

 of a desired optimum. 



The structure of the bordered pits of conifers and its bearing upon the 

 tension hypothesis of the ascent of sap in plants, I. W. Bailey {Bot. Gar., 

 62 {1916), No. 2, pp. 133-142, pL 1, figs. 2; abs. in Jour. Hoy. Micros. Soc. No. 

 6 {1916), p. 572). — The author claims to have shown that in case of Larix and 

 StHjuoia the pit membranes are supplied with perforations of various forms. 

 generally elongated, and of sizes varying from 0.5 /u to 3 m< but the detailed 

 structure of which is obscured by the overhanging and thickened pit borders. It 



