76 Scientific Proceedings, Royal Dublin Society. 



It is much more reasonable to suppose that the fungus present in the 

 wood vessels of the tuber passes from them at some time or other directly 

 into those of the developing sprouts ; and although this passage has not been 

 definitely traced while it is taking place, yet there is every reason to suppose 

 that it does occur. 



There would be considerable difficulty in following the course of the 

 mycelium from tuber to developing stalk while this is actually taking place, 

 particularly because the passage does not appear to occur until after the 

 sprouted tuber has been planted, and the young shoots have made considerable 

 growth. 



During the several seasons over which this disease has been studied, no 

 evidence has been obtained that the presence of the fungus in the tuber 

 interferes with the production of sprouts ; on the other hand, affected tubers 

 have always been found to sprout normally, and to be indistinguishable from 

 healthy ones in this respect. 



According to Miss Dale 1 Verticillium albo-atrum is a cause of " blindness " 

 (non-development of sprouts) in potatoes. It seems clear, however, from 

 her description that this author was not really dealing with this species of 

 Verticillium at all, for it never forms " small rounded segments containing 

 numerous drops of oil," although one of the two new species referred to 

 above does this. The species associated with " blindness " was found in 

 the epidermal and cortical tissues, and not, apparently, in the wood vessels. 

 Further, no infection experiments were made, and it is quite possible that 

 the " blindness " was due to some other cause, while the Verticillium present 

 was simply living saprophytically on the dead tissues. 



The following observations show that the fungus in the wood vessels of the 

 tuber does not pass at once into the developing sprouts. Seven tubers from 

 affected plants were tested in September, 1914, and were found to contain 

 mycelium of V. albo-atrum. They were allowed to sprout in a box during the 

 winter — which they did normally — and remained unplanted till the third 

 week in July, 1915. At this time the tubers were somewhat shrivelled 

 owing to loss of water, and each had produced several sprouts of varying 

 lengths from the eyes situated both near the rose and beel ends of the tubers. 

 A further test was then made of the tubers, and it was found that the 

 mycelium in their vessels was still living. All the sprouts of each tuber 



1 Dale, E., On the Cause of " Blindness" in Potato Tubers. Ann. Bot., vol. xxvi, 



1912, p. 129. I cannot, however, follow Wollenweber, who says (Phytopathology, iii, 



1913, p. 40) that Miss Bale's Verticillium is probably " Periola tomentosa (Fr. ), Reinke 

 and Berthold (1879) [sic] . . . only resembling Verticillium macroscopically. " As far 

 as I have seen it, Periola does not resemble a Verticillium even macroscopically. 



