194 



The Museum Gazette 



ON THE POTATO DISEASE. 



For the benefit of those hitherto uninstructed we may 

 explain that the potato disease is caused by the growth, upon 

 and in the plant, of a minute fungus. This fungus has, like 

 many others, thread-like prolongations which project them- 

 selves within the substance of the stem and leaves to quite 

 indefinite lengths. So long as these do not come to the 

 surface they possibly do not much harm, but, unfortunately, 

 they have a tendency to bud outwards and to produce on the 

 surface what maybe regarded as the flowers of the plant, and 

 when these are formed the portion of the plant on which they 

 occur is killed and becomes black. These " flowers " are 

 easily seen as a delicate white growth on the leaf or corolla, 

 and upon them are formed what we may call seeds with great 

 rapidity and in enormous numbers. These seeds may be 

 carried away in moisture or blown as dust in the air. Each 

 seed is capable of a certain amount of individual movement, 

 and this faculty has gained for them the name of zoospores, 

 that is, spores which behave like animals. They can implant 

 themselves on any suitable plant and may flourish amazingly. 

 They do not in this instance find any plants suitable except 

 the potato and others of the potato family (Solanace&), the 

 black nightshade, bittersweet, the tomato, &c. 



Thus, then, it is clear that a potato plot may become 

 diseased in two different ways. The threads of the fungus 

 may have grown up from the " set " and be, as we have 

 ventured to call it, " flowering-out " on the leaves, or the 

 leaves may have been attacked by dust-blown or rain-carried 

 zoospores. In the one case the disease is acquired, in the 

 other inherited from the parent "set." In the one case we 

 might expect that the lower parts of the plants would be 



