ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 477 



on plants grovra in pots, the pot itself being carefully inclosed in 

 gutta-percha, so that no evaporation of water could take place except 

 through the plant itself. Mr. Henslow's general conclusions are in 

 accordance with those of Wiesner. While obscure heat-rays cause 

 a certain proportion of the loss of water by evaporation, transpiration 

 per 86 is especially, if not entirely, due to those particular bands of 

 light which are absorbed by chlorophyll ; such light, when arrested, 

 is converted into heat, which then raises the temperature within the 

 tissues and causes the loss of water. 



Influence of high Temperatures on the Transpiration-current in 

 "Wood.* — The result of experiments on this subject by Herr C. A. 

 Weber, for the purpose of testing the correctness of the imbibition 

 theory, led to the conclusions that an entire chemical and physical 

 change in the transverse section is without any essential influence on 

 the ascent of the transpiration-current in branches of JRibes ; and that 

 in branches of Gorylus and Samhucus, a disturbance was caused by the 

 withering of the leaves, which could be removed by placing in water 

 of 40°-45^ C. 



Conducting-capacity of Duramen.! — Herr C. Kohrbach has ex- 

 perimented on the capacity for conducting water of the duramen of a 

 number of trees and shrubs. His conclusion is that it has no power 

 of doing this in sufficient quantity. The chief seat of the conduction 

 of water is the alburnum, although the duramen, when present, may 

 be able to assist to a limited extent. 



Imbibition of Wood.| — Prof. E. Godlewski derives the following 

 conclusions on this subject from the results of a series of experiments : — 



1. When wood dries, a decrease of volume takes place from the 

 moment when all the water has disappeared from the cell-cavities ; 

 under perfect desiccation this may amount to 20 per cent, of the 

 original volume. 



2. As wood contracts, the absolute capacity of the cells increases, 

 a fact which points to a stronger contraction of the cell-walls in the 

 radial than in the tangential direction. 



3. When the desiccation of the wood has not advanced so far, the 

 cell-walls absorb, in air saturated with aqueous vapour, as much water 

 as they had previously lost by evaporation, the capacity of the cells 

 diminishes, and the wood again assumes the condition in which it 

 existed before the contraction. 



4. When the desiccation has advanced further, it absorbs less 

 water when brought into air saturated with vapour than it contained 

 before the contraction, but it again assumes its original volume, so 

 that the capacity of the cells has again increased, a proof that the 

 imbibed water is deposited more in the tangential than in the radial 

 direction between the molecules of the cell-wall. 



* Ber. Deutsch. Bot. Gesell., iii. (1885) pp. 345-71. 



t Zeitschr. f. Naturwiss., iv. (1885) pp. 319-47. See Bot. Centralbl., xxv. 

 (1886) p. 105. 



t Verhandl. Polou. Gesell. Naturf. " Copernicus." See Bot. Centralbl. xxv. 

 (1886) p. 236. 



