712 SUMMARY OF CURRENT RESEARCHES RELATING TO 



During droughts photosynthesis is carried on by a chlorophyll-bearing 

 tissue beneath the grey exterior of the stem, and a feeble rate of trans- 

 piration can be detected. The rate of transpiration of Fouquieria and 

 other shrubs varied directly with the water-supply, increasing as an 

 immediate effect of the rains and decreasing as the time past the rains 

 became greater. Accompanying the increase in rate there was always 

 an increase in the transpiring surface, but a decrease in rate occurred 

 without an immediate and corresponding decrease in the transpiring 

 surface, although in the end this always became less. The least rate of 

 transpiration, when leaves were present, was observed during the dry 

 and cool period in the latter part of March, when 0'22 mgm. per 

 100 sq. cm. of leaf surface was recorded. The highest rate was at the 

 end of August, near the close of the summer rains, when the tempera- 

 ture was high (8 "25 mgm. per 100 sq. cm.). A striking adaptation to 

 desert conditions is the promptness with which Fouquieria forms leaves 

 when the water-supply is increased by the rains. The daily periodicity 

 was observed in April. The rate varied in a manner corresponding to 

 variations of the temperature, but not quite the same, and it inversely 

 followed very closely the variation of the relative humidity. 



Relation of Transpiration to Growth in Wheat.* — B. E. Living- 

 ston, as the result of a series of experiments, concludes that total trans- 

 piration of wheat plants grown in various media is as good a criterion 

 for comparing the relative growths in these media as is the weight of 

 the plants. This is explained by the fact that these two criteria van- 

 generally with the weight and area of the leaves. It was evident that, 

 for the types of medium investigated, the amount of transpiration is 

 practically a simple function of the leaf-surface, and that this latter 

 varies quite uniformly with the leaf-weight, which in turn varies with 

 the weight of the entire tops. Thus total transpiration appears to be a 

 measure for the growth of the plant. The nature of the soil or solution 

 in which the roots are grown has little or no influence on those structural 

 and physiological properties of the leaves which control the amount of 

 water lost per unit of leaf -surf ace. The water loss per unit area of 

 leaves is practically uniform throughout the different treatments ; there- 

 fore the variations in total transpiration exhibited are clue not to any 

 difference in structure or activity of the leaves, but simply to the 

 difference in extent of leaf -surface developed. 



Endotropic Mycorhiza.t— I. Gallaud publishes the continuation of 

 his study of endotropic mycorhiza. He takes up the question as to 

 how the hyphae penetrate the cells of the root. They never enter by 

 the hairs ; they envelop the exterior with a fine felt, and here and there 

 penetrate the cells of the host. The growth is always centripetal, and 

 Gallaud does not find that hyphaa grow outwards and spread for the 

 sake of nourishment. The hyphas never enter secretory cells nor 

 chlorophyll-containing cells, in this differing remarkably from parasitic 

 fungi. The writer next describes the microscopic changes in the root 

 induced by the fungus. He does not find any connection between the 



* 



Bot. Gazette, xl. (1905) pp. 178-95 (25 figs, unci diagrams in text). 

 t Rev. Gen. Bot., xxii. (1905) pp. :;]3-2.">. 



