52 DISEASES OF FIELD & GARDEN CROPS. [OH. 



Sclerotium will protrude germ tubes in a few hours if 

 placed in a drop of water. The whole process of growth 

 may be easily watched under the microscope. On germi- 

 nation in water, the filamentous mycelium of which each 

 Sclerotium is formed, protrudes, elongates, and branches in 

 a flexuous manner in all directions ; this spawn is some- 

 times jointed and sometimes free from joints, and whilst 

 in water no farther progress is made in growth beyond 

 the protrusion of these threads. As soon, however, as the 

 mycelium reaches the edge of the water, a change takes 

 place, and the branches become furnished on their tips 

 with minute globose heads, technically termed Sporangia 

 or spore cases. These extremely minute spherical heads 

 at length become filled with elliptic spores or sporidia 

 (so called because they are produced within a spore case), 

 which, on the natural bursting of the Sporangium, or spore 

 case, are set free in the air. The little oval sporidia now 

 soon germinate and reproduce the species. The small 

 mycelial threads protruded from the sporidia are capable 

 of forming little white knots, which at length become, on 

 exposure to the air, the minute black granules termed 

 onion Sclerotia. 



Now, although these small dark-coloured granules will 

 germinate very readily under favourable conditions in 

 water, it must not be supposed that every example germi- 

 nates after a few hours' rest. There can be no doubt that 

 this Sclerotium condition answers precisely the same purpose 

 in the onion as it does in the very large Sclerotium of the 

 potato ; that is, it carries on the life of the fungus in a 

 hibernating state through the winter. 



Individual fungi vary in their habits of growth pre- 

 cisely in the same way as they vary in their specific 

 characters. No hard and fast line can bind down every 

 individual fungus to specific characters or to habits of 

 growth. For instance, in Puccinia mixta, FL, already 

 described, although nine hundred and ninety-nine teleuto- 

 spores out of a thousand may go to rest for several months, 



