648 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



can be used by the plant for its life processes, and since the amount 

 of available soil- water is often decisive for or against a plant's healthy 

 growth, and even its existence, it becomes of great importance to develop 

 a method which will give some measure of this available water. The 

 method generally used is the indirect one of finding the amount of 

 water in the soil when the plant wilts ; this amount is known as the 

 wilting coef&cient of the soil in question, though it really represents 

 the non-available water. Since the wilting coefficient depends upon 

 a want of balance between the rates of absorption and water-loss, and 

 these two processes are readily affected by external conditions, this 

 coefficient varies greatly not only with different soils and different 

 plants, but also with the external conditions. Briggs and Shantz, 

 investigating the relation of the wilting coefficient to soil constitution, 

 came to the somewhat surprising conclusion that for any given soil 

 the wilting coefficient is a constant quantity, independent of the kind 

 of plant or of the external conditions under which it was grown. Cald- 

 well found that this coefficient had different values in experiments 

 made with the same plant under different conditions as to shade and 

 moisture, and therefore showing different rates of transpiration. Prof. 

 Blackman points out that the apparently conflicting results obtained 

 agree in some respects, that the Briggs and Shantz rule cannot be 

 accepted in the generalized form put forward by them, but that it 

 does hold good for low rates of transpiration, so low that probably they 

 fall below those occurring in most plants under natural conditions. 

 But while the trend of recent work has been to show that there is 

 no simple wilting coefficient, it has been shown that the moisture 

 content of the leaves of a given plant gives a simple and satisfactory 

 measure of the plant's condition with respect to water ; the water 

 content of turgid leaves of about the same age varies only within 

 narrow limits for a given species, and this also holds good for the foliar 

 water content at the stage of permanent wilting. The author then 

 discusses the relation of the wilting coefficient to different types of 

 soil, since it is impossible to consider the water content of a soil apart 

 from its physical composition and retentiveness ; and finally he points 

 out the important problems in connexion with the water relations 

 of soil and plant which urgently require investigation. — F. C. 



Errata and Corrigenda. 



Page 135, line 6, for kalomikta read Kalomikta. 



163 ,, 5 ,, Arcenthohium read Arceuthohium. 



239 ,,15 Linneus £QdA Linnaeus. 



257 ,, 5 ,, of read of. 



,, 263 „ 4 „ 1900 read 1899. 



,, 322 ,,2 vulneraria read Vulneraria. 



,, 341 ,,38 ,, deltoidea read deltoides. 



„ liv ,,32 Moupinense read moupinense. 



