82 THE PHYSIOLOGY OF PLANTS 



expense of reserve material which is stored up in the main axis 

 of the plant. This will only take place, however, when an in- 

 crease of temperature stimulates the plant to increased activity. 

 This stimulus, which is so often applied in pot-cultures, may 

 be directly injurious if the newly developed organs, which are 

 always somewhat weakly at the commencement, are not suffi- 

 ciently cared for. This is especially the case with recently 

 formed roots of a sickly plant. As a rule, the pot is kept 

 too moist for the slowly and sparingly developing root system, 

 and as a considerable amount of organic matter is undergoing 

 decomposition in the pot, a dearth of oxygen soon occurs in 

 the soil saturated with water, and the young root-tips decay. 

 In the case of plants which are producing new leaves from 

 reserve substances, it often happens that those plants which 

 are just recovering are placed side by side with and under 

 the same conditions as healthy plants, which require a large 

 amount of transpiration. The new foliage is only able to 

 respond to this great activity if it is aided by an energetic 

 absorption of the root system, as is, for instance, the case in 

 the normal development of leaves in the spring. This, how- 

 ever, is not generally the case with the recovering plants ; 

 consequently the young leaves shrivel up, and the plant will 

 be entirely destroyed. 



In the treatment of plants which are restoring their root 

 system by the production of accessory roots, the first rule is 

 to so reduce the work of the leaves that it is in harmony with 

 the activity of the root. 



This rule is not confined to pot-plants, but applies equally 

 to plants grown in the open. The former may be placed 

 during the period of root development in closed damp houses 

 or frames, so that the amount of their transpiration is reduced, 

 and therefore corresponds with the reduced absorption of the 

 root system. 



In trees and bushes which are transplanted the root system 

 is always injured; the most apparent injury is the absence of 

 the root-tips and of the absorptive region immediately behind 

 them. In the case of such a reduction of the absorptive root- 

 tips, it is evident that the plant would possess too large an 

 amount of foliage if all the branches which had been formed 



