THE ONION-SMUT. 169 



of the leaves is nearly free from mycelium ; but as the disease 

 advances, the mycelium is found in the leaves, bulbs, and 

 roots, — everywhere but in the epidermis. The threads of 

 which the mycelium is composed are transparent, divided by 

 frequent cross-partitions, branch in all directions, and unite 

 with, and are twisted about, one another, so as to form a most 

 intricate network. The mycelial threads are always between 

 the cells of the onion-plant, and never penetrate into them. 

 We have never been able to discover any suckers (haustoria). 

 Of the mode of production of the spores from the mycelium, 

 we shall say a few words later. 



Some of the spores were sown on moist glass slides to 

 ascertain the mode of germination. Those sown in June 

 were kept about three weeks, when they became so mouldy 

 that there was no possibility of being able to observe the 

 germination, and they were consequently thrown away. No 

 change had taken place, except that some of the accessory 

 spores had dropped off from the spore proper. Later in the 

 summer some of the spores were placed on moistened slides 

 and in watch-glasses, where they were allowed to remain for 

 six weeks, when the observations were necessarily interrupted. 

 At the end of that time they had not germinated, although a 

 large share of the accessory spores had dropped away from 

 the spores. It would seem, from these unsuccessful attempts, 

 that germination only takes place after a certain interval of 

 rest of the spores. 



From the brief description just given, it appears that the 

 onion-fungus belongs to the order Uslilaginece, as usually 

 understood, to which also belong the smut of Indian corn, 

 rye, etc. Botanically considered, very little is known about 

 the development of the plants of this order ; but it is not sup- 

 posed that they pass through different stages, found upon 

 different plants, as is believed to be the case with the rust in 

 grain. By smut is generally meant, in this country, Ustilago 

 Mayidis, which causes the smutty ears in Indian corn. The 

 spores of that species, represented in fig. 6, are destitute of 

 the accessory spores found in the onion-smut ; they are much 

 smaller, and are covered with fine points. The onion-smut 

 resembles more closely the smut of rye, Urocyslis occulta, 

 which is common near Boston in the month of June. Fig. 3 



22* 



