216 BOARD OF AGRICULTURE. 



called " the new potato disease," which appeared in the form of 

 small black spots over the surface of the leaves, but a microscopical 

 examination proved that it was only the old eneni}- in a new disguise 

 and appearing much earlier in the season than usual. Nevertheless 

 Mr. Smith called the attention of botanists, both in Europe and in 

 this country, to the fact that the well known parasite had probably 

 under peculiar and unknown conditions presented appearances quite 

 different from what had hitherto been reported. 



Desckiption of thk Resting Spore. 



In making an examination of the black spots on the potato leaves, 

 Mr. Smith placed them with their edges in the water to mascerate 

 them so that the interior of the leaf might be the more readil}' 

 examnied with its contained fungus, but in a few days it was iound 

 that the water greatl}' stimulated the growth of the fungus and 

 before long globular bodies appeared growing from the threads of 

 mycelium within the tissues of the leaf, (Fig. 1.) These globular 

 bodies were not confined to the leaves, but were also found in the 

 stems and in the tubers themselves. They were of two sizes, one 

 about the size of the cells of the leaf, and the other not more than 

 one-fourth as large in diameter. They were developed on small 

 stems here and there from the m3'celium, and when they happened to 

 be near each other it was observed that the}' inclined towards each 

 other until the}' touched, when a small tubular body called the X'olli- 

 nodium was extended out from the smaller bod}' and thrust into the 

 larger, through which more or less of the contents of the smaller 

 ■was poured into the larger, which thus becoming fertilized developed 

 into the long sought for resting spore of the potato- rot fungus. 



The conidia and zoospores are not formed by the union of two 

 elements, but multiply the species by what is called the asexual 

 method of reproduction, while the resting spores — the result of the 

 union of two unlike bodies — represent the sexual method. 



When these resting spores have become mature, the stems upon 

 which they were developed vanish and the spores are set free. 

 After the potato plant has been badly attacked and destroyed b}' 

 the fungus, every part of the plant and its parasite perishes, except 

 the dark brown resting spores just described, and these find their 

 way into the earth and hibernate. When they awake to renewed 

 life in the summer they must germinate in the damp earth, and if 

 no potato plants are near they perish, as the earth cannot support 



