468 SUMMARY OF CURRENT RESEARCHES RELATING TO 



upon temperature and intensity of light, both these factors are of the 

 highest importance. Of equal importance are atmospheric pressure and 

 movements. The rate of diffusion is proportional to the distance 

 between the surface and the mesophyll-cells containing the largest 

 amount of vapour. The resistance offered to transpiration by the 

 epidermis is negligible. In windy weather transpiration is 2 to 5 times 

 as great as in quiet air ; when there is no wind the transpiration is in 

 proportion to the radius of the leaf, but in windy weather it is propor- 

 tional to the surface of the leaf. Experiments show that in quiet air 

 the cavities are filled with air saturated with aqueous vapour, and the 

 epidermis, not the mesophyll, appears to be the limiting factor. Any 

 condition which tends to narrow the openings of the stomata tends to 

 lessen transpiration, and the same result is attained by the sinking of the 

 stomata and the cuticularisitig of the deep air-cavities. Xerophytes, 

 when exposed to wind, showed a difference of ?>0 to 70 p.c. of transpira- 

 tion less than ordinary plants. Assimilation is affected by all the above- 

 mentioned factors, but in a less degree than transpiration. 



Function of Living Cells in Ascent of Sap.*— P. A. Roshardt has 

 experimented with 127 species belonging to the genera of 48 natural 

 orders, representing both Monocotyledons and Dicotyledons, in order to 

 discover whether the living cells of herbaceous plants have any connec- 

 tion with the ascent of sap. Stems, branches, twigs, and leaf-stalks were 

 used, and certain portions were killed by means of steam, ether, or xylol. 

 The author comes to the conclusion that there is no difference between 

 high trees and low growing plants as far as sap ascent is concerned. 

 The experiments in 125 cases tend to show that living elements are 

 necessary for the transport of water in stems and in leaf -stalks. _ The 

 current continues for some time after the living cells of any particular 

 region have been killed, but it is less, and in the case of leaves is made 

 evident by withering. If the destroyed region is large the result is even 

 more marked. Usually young plants suffer more than older ones from 

 such treatment. No change in the conducting apparatus itself was 

 caused by the experiments, and the withering could only be ascribed to 

 the destruction of the living cells. There is no reason for accepting 

 Ursprung's theory that the' living cells tend to prevent lateral loss of 

 water. It is not yet evident which tissues of living cells are of the 

 most importance in promoting the ascent of sap. 



CRYPTOGAMS. 



Pteridophyta. 

 (By A. Gepp, M.A., F.L.S.) 



Morphology of Phylloglossum.t — H. F. Wernham gives an account 

 of the morphology of Phylloglossum Drummondii and discusses the 

 meaning of its structure. He briefly summarises his conclusions thus : 

 1. Phylloglossum shows anatomical signs of being, like Tmesipteris, 

 " micropliyllous " below, and " megaphyllous " above, thus being inter- 

 mediate between the Pteropsida and Lycopsida of Jeffrey. 2. The 



* Beih. Bot. Centralbl., pp. 243 -357 (2 figs.). 

 t Ami. Bot. xxiv. (1910) pp. 335-317 (figs.). 



