504 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



east, but exposed to the same amount of rain and sunshine, and, therefore, 

 scorching, the leaf spotting could not be found. 



The suggestion, therefore, that climatic conditions were directly 

 responsible for the trouble seems to be put entirely out of court; and 

 this being so, it is obvious that the fungus was not growing upon 

 already dead tissue, but attacked living tissue and caused its death. 



This somewhat long discussion of the direct connection between 

 the injury to the leaves and the weather, seems called for on account of 

 the frequency of the ascription to this cause of injuries to plants that 

 are directly attributable to other, and often preventable, causes. 



The question next arises as to whether there were any climatic 

 conditions prevailing during the period that might contribute to the 

 weakening of the foliage, and so lay it open to the attacks of a fungus. 



Climatic conditions apt to lead to abnormal or weak development 

 include — 



(1) Too little moisture in the soil ; and 



(2) the converse, a water-logged condition of the soil ; 



(3) a low soil temperature, preventing the ready absorption of water 

 by the roots ; 



(4) too great a degree of direct sunshine on the young leaves ; 



(5) too little sunshine, checking transpiration ; 



(6) too great a degree of moisture in the air, checking transpiration, 

 and, if combined with a high temperature, leading to the development of 

 large soft foliage ; 



(7) too low a temperature, checking transpiration, assimilation, and 

 growth ; 



(8) drying winds, causing too great an amount of evaporation. 



The following particulars will show which of these conditions 

 obtained during the period in question. 



Taking the several points in the order given above, we find, in the 

 first place, that the average rainfall during the months from October 

 to May inclusive at Wisley is about 15 inches, and the actual rainfall 

 during these months in 1906-7 was 18*03 inches. The soil was there- 

 fore not deficient in moisture. 



(2) Neither, bearing in mind the well-drained condition of the Wisley 

 apple plantation and the light nature of the soil, can the soil have been 

 water-logged. 



(3) The mean soil temperature at the depth of one foot during the 

 period in question was over 51° and never fell, as the accompanying 

 temperature chart (fig. 90) shows, below 47°. Such a temperature 

 would not adversely act upon the power of absorbing water by the root- 

 hairs, and does not vary appreciably from the normal for the period. In 

 190G the mean at a depth of one foot was 51*8, and in 1905 53-4. 



(4) The amount of bright sunshine recorded during the period was 

 208*5 hours, which compares with 223*7 hours in 1906, and 291*7 hours 

 in 1905 for the same period. An excess of bright sunshine could scarcely 

 have been a contributory cause ; rather it would appear 



(5) there was a deficiency. Indeed, on each of eighteen days there 

 was less than three hours of bright sunshine, compared with thirteen 

 such days in 1906, and eight in 1905. 



