1914] CURRENT LITERATURE 535 



decline in evaporation each year in plants whose water supply is not replenished 

 is attributed in part to increasing concentration of the cell sap; in the cacti 

 this increase was from i to 3 per cent. From 60 to 70 per cent of the max- 

 imum water-balance may be lost by cacti without impairing the power of 

 recovery and subsequent growth. It is suggested that a detailed chemical 

 study of these plants is needed, it being felt that their high osmotic activity 

 and their great acidity resulting from modified photosynthesis are insufficient 

 to explain the origination of the habit of accumulating and retaining large 

 water-balances. — H. C. Cowles. 



English woodlands. — As would be expected, very few of the English wood- 

 lands are primeval. Such woodlands may still be found, however, near the 

 upper forest limits in mountainous regions. 9 Most English woodlands arc- 

 to be regarded as semi-natural, that is, the trees are felled somewhat regularly, 

 but the reproduction, either from seeds or suckers, is natural. New forest 

 plantations are distinguishable from natural or semi-natural woodlands by 

 the presence at times of exotic tree species, and almost always by the absence 

 of a representative woodland ground flora. Three main series of woodlands 

 are recognized, the alder-w r illow series of wet soils, the oak-birch series of sili- 

 ceous soils, and the beech-ash series of calcareous soils. The series are further 



divided into associations. 



Adamson has made an intensive study of Gamlingay Wood in western 

 Cambridgeshire, one of the semi-natural woodlands noted above. 10 The 

 wood is on bowlder clay, part of which is calcareous and part non-calcareous; 



the trees on the former are oak and ash, while the ash is absent on the latter. 

 Although it is noted that there are intergradations, it is observed that the herb- 

 age in the two woodland types is different; the dominant forms in the sili- 

 ceous woodland are Pteris aquilina and Holcus mollis, whereas those of the 

 calcareous woodland are Spiraea Ulmaria, Mercurial is perennis, Deschampsia 

 caespitosa, and Fragaria vesca. Little attention is paid to successional features. 

 It is believed by the reviewer that more thorough successional studies would 

 tend to break down some of the distinction between calcareous and siliceous 

 woodlands, as recognized by English ecologists; it seems almost certain that 

 an original underlying soil must more and more lose its influence on vegetation, 

 as humus accumulates. Careful studies were made by Adamson of evapora- 

 tion, soil moisture, and other factors. 



In connection with the above it may be noted that Tansley and Adamson" 

 have given an account of some observations made in some Gloucestershire 



9 Moss, C. E., Rankin, W. M., and Tansley. A. G., The woodlands of England. 



New Phytol. 9:113-149. 1910 



n 



Adamson 



Jour. 



Linn. Soc. Bot. 40:339-387. pis. tf. 191 2. 



"Tansley, A. G.,and Adamson, R. S., Reconnaissance in the CotteswoWs and 

 the Forest of Dean. Jour. Ecol. 1:81-89. 1913. 



