RECENT ADVANCES IN SCIENCE 561 



to deteriorate both on account of the continuous cropping and 

 the leaching of the surface. The best type of Hill pasture 

 (Agrostis, Festuca, Cynosurus) is associated with flushes, where 

 the water contains lime in solution, and where moreover move- 

 ment of the surface water ensures good aeration and, in times 

 of spate, brings about a dressing of silt. By open drains the 

 flush grassland can be extended provided the stream water is 

 " hard," but the " soft " water from peat has a reverse effect. 

 Pteris aquilina is commonly associated with flush grassland, 

 but is kept in check by the trampling of cattle, and can be 

 suppressed by repeated cutting or spraying. Heather grown 

 for fodder should be burned at least every fifteen years. Rough 

 pasture of Nardus stricta, Molinia ccerulea, and Juncus squar- 

 rosus has a low feeding value, but can be improved by thorough 

 grazing and repeated burning at intervals of two to three years. 

 The author points out that improvement depends almost 

 entirely on an increase in available labour. 



PLANT PHYSIOLOGY. By R. C. Knight, D.Sc, Imperial College of 

 Science and Technology, London. (Plant Physiology Committee.) 



Transpiration. — The diversity of the direction of modern 

 studies of transpiration is an excellent indication of the realisa- 

 tion, which has been forced upon researchers, that the problem 

 of the movement of water through a plant is a rather more 

 complex question than it was formerly considered to be. Much 

 progress has been made from the stage when transpiration, 

 admittedly of vital import in the life process of the plant, was 

 considered to be adequately explained as a process resulting 

 from root-absorption and evaporation from the leaves " at 

 the discretion of the stomata." The conditions affecting the 

 transpiration stream have been studied at every stage of its 

 progress, and factor after factor has been successively added to 

 the list until the stomata themselves cut but a poor figure in 

 the array of regulating influences. In fact, in the opinions of 

 some workers stomatal action is normally negligible compared 

 with the controlling activities of other factors. It is recognised 

 that external conditions, as represented by the soil and the 

 atmosphere, as well as the internal conditions peculiar to the 

 plant, exercise an important regulating influence. 



The question of the water supply from the soil has been 



