1002 JOURNAI, OF FORESTRY 



(b) Both absorption and conduction capacities are developed only on the low 

 scale. 



(c) The leaves shovi^ no adaptation calculated to aid in extending their trans- 

 piration towards the limit of capacity. On the other hand they are commonly 

 protected by cuticle and other means against excessive water-loss. 



(d) Shade leaves have a greater internal surface relative to their mass than 

 sun leaves. This does not appear to be a transpirational adaptation, but as the 

 illumination is very slight, it may be better interpreted as a means of increasing 

 the CO2 absorption capacity, the percentage of carbon dioxide in the forest air 

 being supernormal. 



(e) It has been found that the average of intercellular space in leaves ex- 

 amined in Brazil corresponds closely to that found in Europe. This may be 

 associated with the constancy of leaf function over the whole world and the 

 corresponding constancy of atmospheric constitution. 



(f) Lack of capacity to increase the transpiration current under the stimulus 

 of sun-fliecks, wind, etc., leading to the necessity of protective devices, seems to 

 point to edaphic factors antagonistic to absorption. 



(g) Whether the suppression of foliar evaporation signifies the suppression 

 of a water current in the axis does not appear. It is not impossible that a slow 

 current is maintained by root-pressure, enough to satisfy the demands of elas- 

 tic growth and of CO2 assimilation, which between them utilize the major por- 

 tion of the water supply, some part of which also returns through the phloem 

 or may eventually be excreted in the fluid state. 



In such circumstances the measurement of water-loss v^ould give no 

 indication of the absorbing capacity of the plant, of which it would be 

 quite independent. J. W. T. 



McLean, R. G. : Studies in the Ecology of Tropical Rain-forest, with Spe- 

 cial Reference to the Forests of South Brazil. The Journal of Ecology, Vol. 

 VII, Nos. 1 and 2, pp. 5-54, May, 1919. 



SILVICULTURE, PROTECTION, AND EXTENSION 



The problems centering in succession are be- 

 Begmmngs of . , , , ... 



'^ . commg more and more problems 01 basic mter- 



. est to the forester. Through complete or partial 



• T/ 77 denudation vast areas are annually brought into a 



condition where vegetation must begin its long 

 process of bringing back the climax forest. It may be of beech and 

 maple or of spruce and pine. How long nature takes to clothe a com- 

 pletely denuded soil or a new soil with forest vegetation necessarily 

 depends upon local conditions and the circumstances surrounding each 

 case. The time required, however, is of particular importance in 

 American forestry, due to the vast areas of forest annually denuded by 

 fires and partially denuded by our destructive methods of lumbering. 



