MULBERRY-DWARF TROUBLES IN JAPAN. 



21 I 



But we must here remember that the power of resistance to 

 the disease is not absolutely confined to certain fixed varieties, but 

 may be gradually changed by climatic conditions, soil, and 

 treatment. Thus we always observe that, when certain varieties 

 are induced to rapid growth by the addition of soluble manures 

 in excess, and then cut, then even the fav r ored varieties may be- 

 come diseased, while on the contrary, such varieties, as 

 Takasuke, will never become diseased if they are cultivated in 

 infertile soil with poor manuring. Thus, one and the same 

 variety may undergo a very remarkable; change in its character, 

 especially as regards its conduct towards the disease. Over- 

 growth accelerates the migration of reserve materials. If the de- 

 velopment of new shoots after cutting is very energetic, then the 

 want for reserve materials must be correspondingly great, and the 

 absorbed nutriments must be insufficient for the demand, the re- 

 sult being an emaciated condition of the shoots. Over manuring 

 will never directly increase the quantity of reserve materials in 

 the roots and stems in the growing periods, the nutriments 

 supplied as manures being all transported to the growing parts. 

 So if we cut such over-grown plants, the new shoots will 

 develop more energetically and the reserve materials will soon 

 be exhausted, just the natural condition for the disease. Thus 

 we can understand why the power of resistance to the disease is 

 not absolutely confined to certain fixed varieties. Young plants 

 are rarely attacked ; this may be explained by the fact that the 

 cells of young plants are more active, and after cutting can 

 develop small rootlets more easily, and thus gain a stronger 

 absorptive power, than old plants, so that they can easily 

 recover from the deficiency of reserve materials. 



Old plants are less active, and after cutting, the develop- 

 ment of new rootlets takes place with more difficulty, and accord- 

 ingly, their absorptive power must remain comparatively station- 

 ary and the recovery will consequently be slower. 



For the same reason, the disease appears oftener after cutting 

 in late summer or autumn, while it is less frequent when the 

 plants are cut earlier. The development of new rootlets and the 

 consequent recovery after cutting, must be much more difficult 

 in autumn. 



The young rootlets must once lose their activity after 

 cutting, and the entire root-system will become gradually ineffici- 



