xxxvi.] POTATO DISEASE, II. PASSIVE STATE. 325 



which, in every instance, was apparently perfectly intact. 

 Another instructive case is given in the Gardeners' 

 Chronicle for 1st March 1884, p. 283. 



Mr. Jensen states that it may be said with full certainty 

 that the disease either never reaches the tuber by growing 

 through the stems, or, if it does so happen in a few single 

 plants, which he says, to his knowledge, has never been 

 proved, it is of so rare an occurrence as to be of no prac- 

 tical consequence. 



A series of test experiments has been instituted this 

 year at the garden of the Royal Horticultural Society at 

 Chiswick, where Mr. Jensen's instructions will be rigidly 

 adhered to. At the time of planting, when some of the 

 tubers were cut for sets, it was observed that the disease 

 was apparent in the interior, with no trace whatever of 

 disease on the skin or bark. The bending over of the 

 brittle haulm we consider a delicate operation, which is 

 hardly suited for unskilled rustics ; and if the easily- 

 broken stems become severed instead of bent, the process 

 becomes identical with the old plan of removing the haulm 

 altogether. A broken haulm is synonymous with the 

 destruction of leaves, and if the leaves are lost no starch 

 can be formed for subsequent storage in the tubers. The 

 mere gathering of the stems together for bending over 

 must be injurious to the potato plant, as it prevents the 

 leaves from receiving their requisite amount of light. 



We consider the immunity from disease of earthed-up 

 potatoes, with bent haulms, is less owing to the power 

 possessed by the earth of filtering the fungus spores, and 

 so preventing them from reaching the tuber, than to the 

 effect of the earth in keeping the tubers whole and sound. 

 Mr. Jensen has also devised what he terms a disinfecting 

 apparatus. This has been described and illustrated by 

 Mr. C. B. Plo wright in the Gardeners' Chronicle for 5th 

 April 1884. According to Mr. Jensen, a temperature of 

 77 F. kills both the mycelium and spores of the Perono- 

 spora, provided the heat be continued for a sufficient 



