Feb. 1891.] BOTANICAL SOCIETY OF EDINBURGH. 65 



Potato Disease and Paeasitism. By A. Stephen Wilson, 

 North Kinmuiidy. 



In The Gardener's Chronicle of October 7, 1882, I pub- 

 lished an account of certain bodies I had discovered in the 

 under side of the leaves of the potato, in all parts of the 

 stems, but especially near the nodes, and in the tubers, 

 especially around the eyes. These bodies I provisionally 

 called sclerotiets, believing them to be analogous to the true 

 sclerotia of various fungi. From subsequent observation and 

 consideration, I have seen reason to alter my first views ; 

 and I now propose to call these bodies granules of muco- 

 plasm. They are translucent microscopic globular bodies, 

 coated with oxalate of lime, and infest all parts of the 

 potato-plant, and are also to be found profusely under 

 the skin of the tomato. My observations seem to authorise 

 me to say, that from these granules in germination arises 

 the mycelium of Feronospora infestans, and thus the 

 disease in the tissue of the potato may break out at any 

 part of the plant, or at all parts simultaneously, without 

 translocation. Those granules of mucoplasm may be best 

 seen in an early stage by germinating resting-spores on a 

 glass slide ; from the threads of mycelium arising from 

 these there are exuded along the sides of the threads masses 

 of granular plasm, and in those masses, after a while, the 

 grains assume a globular form, and throw out fresh threads 

 of mycelium — the granules are, in fact, equivalent to spores. 

 Now, as the resting-spores are not parasitic, but live and 

 germinate in the soil or in any dead matter, it is contact 

 with the mucoplasm exuded from their fresh mycelium which 

 originates the parasitism of P. infestans in the potato. And 

 I think there are various analogies to warrant the conclusion 

 that it is the invasion of the potato-plant by this parasite 

 which is really the cause of the potato-tubers themselves. 

 Various botanists have held that tubering in such plants is a 

 mark of a diseased condition. I shall mention only one 

 analogy. The galls called Devonshire galls, which grow in 

 great numbers sometimes on the buds of oaks and some 

 other trees, are simply fleshified buds ; the leaves, instead of 

 spreading out into a thin palm, become inspissated with the 

 juices of the tree, and are thus agglomerated into a globular 



TRANS. BOT. SOC. VOL. XIX. E 



