BOOKS .'U^D CURRENT LITERATURE 261 



sions can be briefly given although a study of the papers will be neces- 

 sary if a background for the results is desired. 



At Pusa the following are some of the effects of poor soil aeration 

 noted on the monsoon crops. The summer crops are heaviest when 

 the monsoon rains are below the average and well distributed. The 

 surface skin which forms on the soil as a result of these storms checks 

 growth; breaking the crust benefits crops immediately. Howard 

 concludes that in the Pusa region the want of sufficient air in the soil 

 does infinitely more harm to the monsoon crops than the want of water. 

 So far as the crops of winter are concerned, analogous results are to 

 be seen. Although relatively small in amount, the rains of winter also 

 cause the formation of a crust on the soil, which interferes with shoot 

 growth, and when this crust is broken the activities of the shoot are 

 restored to their normally healthy condition. Possibly, however, the 

 most striking result of poor soil aeration on the growth of shoots was 

 observed in connection with established trees. A resting period occurs 

 during winter when leaf-fall is common. With the rise in temperature 

 that takes place in February, new leaves are formed, and flowering 

 and shoot growth occur. Rapid growth goes on until the hot weather 

 supervenes. At the commencement of the monsoon phase another 

 period of growth takes place, but with the saturation of the soil growth 

 slows down or nearly ceases. It is not renewed until the end of the 

 monsoon, when with the drying out of the soil better aeration results. 

 Growth is then renewed for the second time and goes on until the advent 

 of cold weather. Although the soil temperature is favorable in summer 

 and there is an abundance of moisture, the vegetative activities are 

 greatly diminished owing to the want of oxygen or the presence of a 

 harmful amount of carbon di-oxide. The immediate effect of inade- 

 quate aeration of the soil is wilting, which has sometimes been treated 

 as a disease. 



Numerous cultural experiments show that the effects exerted on 

 shoots by poor soil aeration affect the roots primarily. Thus, any 

 method by which good aeration is produced restores the healthy con- 

 dition of the crops, or prevents the injurious effects attendant on an 

 inadequate air supply. 



The fact that variation in soil aeration directly influences root 

 growth is shown also in another manner by the behavior of gram under 

 different soil conditions. When grown in three sorts of soil within 

 100 yards of each other and all well moistened, characteristic differences 

 in the development of the root-systems of the plants were observed. 



THE PLANT WORLD, VOL. 20, NO. 8 



