522 EXPEEIMENT STATION EECOED. 



The role of winter temperatures in determining' the distribution of plants, 

 F. Shreve (Amct: Jour. Bat., 1 (WU), No. 4, pp. 194-202, fig. J).— The author 

 has carried out some preliminary investigations on the importance of the tem- 

 ])erature phases of the past season in determining the distinct distributional 

 limits of some subtropical desert plants. 



Studies previously noted (E. S. R., 25, p. 732) with succulent plants native 

 to various altitudes in southern Arizona, indicate, it is claimed, that within 

 the limits of the species tested the number of hours that they are exposed to 

 temperatures below freezing determines their survival or death without regard 

 to the absolute minimum reached during the freezing period (although minima 

 below 18° F. were not used). It is stated also that the succulents which have 

 the lowest vertical limit of distribution are unable to resist freezing for more 

 than 19 to 22 hours in duration, while species of higher limits are progressively 

 able to withstand longer periods of freezing, up to about 66 hours, but that 

 Opimtia missouriensis withstood 375 consecutive hours of freezing at Havre, 

 I\Iont., in 1910-11. It is suggested that further studies in this direction may 

 furnish a knowledge of the underlying ciiuses of the phenomena of distribution. 



The wilting- coefficient of the soil, V. H. Blackman (Jour. Ecology, 2 (1914), 

 No. 1, pp. 43-50). — This is mainly a review of some recent contributions dealing 

 with soil moisture in relation to plant needs as affected by the various factors 

 involved, in particular an article by Briggs and Shautz (E. S. R., 26. p. 628). 



Changes produced in the sap by the heating- of branches, H. H. Dixon 

 (Sci. Proc. Roy. DuhUn Soc, n. ser., 14 {1914), No. 15, pp. 22.^-228).— Compari- 

 sons were made of the sup of branches killed by heating with steam in the case 

 of beech, poplar, and Ilex, and it was found that the steaming brought about a 

 change in the depression of the freezing point, a decided increase in conductiv- 

 ity, a marked increase in acidity, a change in color, and the destruction of oxi- 

 dase. The sap of steamed branches from a number of different species of plants 

 was centrifugally extracted and tested on the leaves of Elodea canadensis, 

 comparisons being made with fresh sap. In nearly every instance destructive 

 changes were brought about in the leaves within two or three days. 



The evidence drawn from these experiments indicates that leaves above a 

 steamed branch perish not because they are cut off from their water supply, but 

 because profound changes have been produced in the sap, resulting in the pro- 

 duction of poisonous substances. The drying of the poisoned leaves is believed 

 to be caused by the partial or complete plugging of the water channels by 

 colloids exuded from the heated cells or coagulated in the sap. 



The role of glycerin in causing anomalous structures in Pisum sativum, 

 J. Laukent {Bui. Soc. Bot. France, 60 {1913), No. 7, pp. 592-601, pis. 3).— The 

 author describes certain anomalous structures of peas grown in culture solu- 

 tions to which glycerin was added. In studying peas grown in such solutions it 

 is said to be difficult to recognize asparagin, as that substance is transformed 

 into albuminoid material as rapidly as formed. With plants having a less abun- 

 dant nitrogen reserve than the Legumiuosse, and grown in cultures containing 

 glycerin and asparagin or glycerin and peptone, these substances offer material 

 for the synthesis of albuminoids, and some not only favor growth, but often 

 jtroduce a multiplication of cells and other unforseen anomalies. 



The spur shoot of the pines, R. B. Thomson {Bot. Gaz., 51 {1914), No. 5, 

 pp. 362-385, pis. 4, figs. 2). — Giving an account of studies by himself as well as 

 some views held by other authors on the deciduous spur shoot of the genus 

 Pinus, the author considers the facts as noted on a study of both fossil and 

 living pines as practically conclusive evidence regarding the specialized char- 

 acter of this structure. The spur, as it stands to-day, is considered a special- 



