68 Scientific Proceedings, Royal Dublin Society. 



of the disease then would appear to be essentially similar, the principal 

 difference being that in type B the mycelium of the fungus takes somewhat 

 longer to reach the plant from the parent tuber than is the case with type A. 

 Type C is stated to arise exclusively when tubers derived from plants 

 affected with either type A or type B of the disease are planted, although 

 such tubers may also give rise to " misses," i.e., may produce no plants at all. 

 Plants affected with type C of the disease come above ground late, develop 

 slowly, and remain small. The leaves do not expand fully, and are not of the 

 normal green colour. The leaflets are curled and wavy, the petioles being 

 bent backwards. Death and desiccation of the plants take place from above 

 downwards, and after the death of one stalk others may subsequently develop 

 from the same tuber, but only to die away in their turn. The stalks are 

 exceedingly brittle, and the plants are said to die without producing any new 

 tubers, so that the disease exhausts itself in this, the second, generation. 1 No 

 fungus mycelium is present in the vessels of plants of type C at any time ; 

 but the mycelium of V. albo-atrum is stated to be present in the cortical 

 tissues of the subterranean portion of the stalks. The seed-tubers producing 

 this type of the disease, when they have not already rotted in the ground, 

 contain no mycelium in their internal tissues ; but Verticillium is stated to be 

 present in the cells of the skin, although it does not penetrate into the 

 subperidermal tissues. 



What strikes one as rather remarkable in Beinke and Berthold's account 

 of the disease is the absence of the fungus from the wood vessels in types B 

 and 0, and, as has already been surmised, this may possibly be due to the fact 

 that a long enough period was not allowed to elapse before the examination 

 was made. 



Much stress is laid on the point that the fungus is only present at the 

 very heel-end of the tubers derived from plants affected with the A and B 

 types of the disease, and that even at the end of the season when such tubers 

 had produced plants of the C type mycelium could not be found in their 

 interiors. 



The mode of transmission of the fungus from the first generation (A and 

 B types) to the second (0 type) is, as described, a most peculiar one. It is 

 stated that when the tubers having the mycelium strictly limited in location 

 to their heel-ends are planted in the spring the mycelium grows around the 

 outside of the tuber in the cork layers of the skin, and without penetrating 

 the interior. Having in this way reached the bases of the young sprouts, it 



x In a postscript it is stated that in a few cases tubers from plants affected with the 

 A type of the disease gave rise to plants of the B and not of the C type ; hence it is assumed 

 that in such cases the disease would become exhausted in the third generation. 



