MULBERRY-DWARF TROUBLES IN JAPAN. 285 



the principal cause of the disease is never of parasitic nature. It 

 is exclusively the cutting in the growing' season that causes the 

 disease. Small rootlets which develop vigorously in the growing 

 season can only support their activity by the supply of organic 

 nutriments furnished by the leaves. Therefore the cutting off 

 of the branches and leaves in the growing season stops the 

 supply of food to the roots. At first the small rootlets starve 

 and die off. New rootlets however come forth again after the 

 new shoots had reached a certain height and acquired power of 

 assimilation. 1 have calculated that the new shoots coming 

 from the cut stocks, rely upon the reserve material in the roots 

 even as long as 40 days after cutting and until they have 

 reached the height of 50— 60 cm. Therefore it is very evident 

 that if the new shoots had used up all the reserve materials 

 in the roots before the development of new rootlets which can 

 absorb the soil nutriments freely, then the new shoots must 

 naturally suffer from starvation and disease must be the final 

 result. I have proved this fact experimentally by examining 

 the state of root development during the last summer. In the 

 beginning of June, when the leaves were in full development, 

 the growth of roots was very marked and small rootlets (so 

 called while roots) were well developed forming a net work. 

 After cutting in June (June 5— lo) the growth of these rootlets 

 was completely stopped and the white fresh appearance gra- 

 dually turned yellow and reddish brown and finally the roots 

 decayed. Even 30 days after cutting, no development of new 

 rootlets was yet observed, while the development of the rootlets 

 of the plants not cut was more and more advanced. In two 

 weeks from cutting new shoots had developed and reached 

 50— 60 centimeter in four or five weeks, but new rootlets were 

 not yet visible. Later on they gradually appeared but were 

 very scanty and until autumn they failed to achieve the normal 

 development. These facts were observed with many varieties 

 and under different conditions and agree perfectly well with my 

 former assumption that the new shoots developing almost directly 

 from the roots rely upon the reserve materials in the roots even 

 after reaching the height of 50 — 60 cm. Thus it is very evident 

 that the exhaustion of reserve materials may very often take 

 place before the new shoots can be provided with new mineral 

 nutriments from the soil and this circumstance again retards 



