386 Degeneration in Potatoes. [oct., 



and averaged from 50 to 60 per cent. Investigations made 

 by Dr. Schleh and Dr. Speikermann proved the absence of any 

 specific disease, and the failure was in part attributed to the 

 practice of growing the same kind of potato from sets produced 

 on the spot for a long period of time. 



In France Dr. Delacroix* has described the occurrence, on 

 a large scale, of a similar sterility of potato tubers, which he 

 calls " filosite." In this case the few sprouts produced become 

 considerably elongated, remain very slender, and usually do- 

 not appear above ground, and when they do so, produce only 

 a few small stunted leaves. Here again there was an absence 

 of disease, and the author considers that " filosite " is due to 

 decadence and loss of vitality, brought about by the employ- 

 ment of the vegetative method of reproduction invariably fol- 

 lowed. In those countries where attention is paid to the pro- 

 duction of improved varieties of potatoes, certain points have 

 been constantly kept in view. Amongst such may be enume- 

 rated : increase of crop ; improved flavour ; smooth and even 

 surface ; immunity from disease. With the first three points 

 cultivators have surpassed their most sanguine expectations,, 

 and it is hoped that by a strict application of Mendelian laws, a 

 strain of potatoes immune to all ills will shortly be forthcoming. 



Unfortunately the method of selection and the lines followed 

 in producing these much desired improvements in potatoes 

 have in some instances also favoured other unexpected modifica- 

 tions, which have resulted in sterility or failure to form sprouts 

 by the tubers. This failure has been shown, by a series of 

 experiments conducted at Kew and extending over three years, 

 to be accompanied by a combination of two distinct specific 

 conditions : (i.) more or less arrest of the development of the 

 vascular system of the tuber ; (ii.) comparative absence of the 

 ferment or enzyme called diastase from the tuber. 



A tuber, as is well known, is the very much swollen terminal 

 portion of an underground branch specialized for the purpose of 

 a vegetative method of reproduction. Such tubers retain, 

 under normal conditions, those structures present in the above- 

 ground stem of a potato plant. The main bulk of a tuber 

 consists of a mass of tissue crowded with starch, which is used 

 up in the formation of new shoots or sprouts. This starch is 



*Comp. Rend., Dec, 1903, p. 1,006. 



