— 32 — 



layer, lies the intermediate dry layer, containing only about 10"/,, of use- 

 less water which is not shown on the diagrams. If the upper humid 

 belts have not got into the proper condition requ'red of a normal root- 

 inhabiting layer (110 to 140 cm.) the roots developing therein always 

 meet with an insurmountable barrier, the intermediate dry layer; for they 

 cannot penetrate into this dry sphere void of useful water. 



We saw above that the most essential factor for a good crop ofan- 

 nual plants, whose root-systems do not reach so very deep (100 to 

 150 cm.) is the thickness of the humid superficial layer. Perennials- 

 clover, shrubs, trees— differ is that respect. Their root-system must 

 penetrate several fathoms deep in order to enable the plant to develope 

 normally. 



If the intermediate dry layer is injurious to cultivated annuals, pre- 

 venting full developement of the under ground parts when the upper 

 humid layer is less than the root-inhabited layer and the root-system, 

 cannot develope normally, then the effect of the intermediate layer on 

 perennials is to exclude every possibility of their culture. Annuals may 

 develope luxuriously if their root-inhabited soil layer (to 150 cm.) is 

 mo'st. Per ennials, which develope their root-systems during many 

 years, extending them for several fathoms, must have moist soil in the 

 whole of the depths they penetrate. And if they meet an intermediate 

 dry layer in consequence of which their roots (the upper lateral roots 

 turn downwards after several months and do not differ in size from the 

 main roots) cease their growth, the lateral roots commence to increase 

 their developement. The humid layer gets crowded with a network of 

 side roots which rapidly consume the reserve of useful water and by au- 

 tumn the whole root-inhabited layer dries up-the plant neverthelless 

 continnes to vegetate weakly far into autumn. 



In the following spring the strongly developing lateral roots com- 

 mence early to exhale large quantities of water and by the end of may 

 or the begining of June all the reserve water is expended. Thus the 

 plant, in the second year of its existence, has to live through the hottest 

 summer period, v/hen useful water is absolutely necessary owing to the 

 heightened process of evaporation, in soil which has become dried up. 

 Usually the plant cannot outlive this period and perishes. 



The systematic failures experiences in cultivating perennial edible 

 herbs and trees in dry steppe places can only be explained thus; that 

 these plants are treated under conditions only suitable to annual plants. 



A perennial plant cannot satisfy itself with the upper humid layer 

 above; it must be able to stretch out its roots into the lower permanent 

 humid layer which, uninterrupted by dry belts capable of arresting the farther 

 downward progress of roots, extends to a depth sufficient for the roots of 



