ONION SMUT FUNGUS. 117 



the spores. Within twenty-four hours slender tubes of about half the diam- 

 eter of the original cells could be observed growing out from them. These 

 tubes originate from one or from both ends of the cell, quickly become 

 septate and branched, and within three days each is the center of a white 

 mycelium which can be seen with the naked eye. The centrifugal empty- 

 ing of the cells, the branching, and all other characters are the same as 

 those of the growths from the chlamydospores. Practically 100 per cent 

 germinated. No conidia could be found on them at anj^ stage. The de- 

 velopment of these cells is represented by Fig. 2, D. 



Taken in connection with the fact that no true conidia have appeared 

 in any of the cultures, the conclusion seems warranted that these cells 

 detached by division of the vegetative hyphse are analogous to and serve 

 the same purpose as the sporidia (conidia) of other smut fungi in propa- 

 gation and dissemination. In fact, almost any cell of the mycelium which 

 retains its protoplasm is a potential spore, and may serve all the functions 

 of the same. Since the cells are so easily detached and germinate so quickly 

 and universally, their importance in the distribution of the disease can 

 hardly be overestunated. 



Life in the Soil. 



There are at least two ways in which the organism may pass from the 

 host into the soil; (1) when the spores are mature and the sorus is exposed 

 by rupture of the enclosing host tissue, the spores fall out or are blown or 

 shaken out by various agencies and fall to the ground; (2) as previously 

 described, mycelium from any buried lesion may grow from the disinte- 

 grating tissues directly into the surrounding soil. It has also been indicated 

 in cultures on soil extract media that the soil contains all the elements 

 necessary to induce germination of the spores and to nourish the mycelium 

 into further growth. In order to study further this period of development 

 of the organism, pure cultures on soil were made by inoculating Ehrlen- 

 meyer flasks of sterilized soil, some by placing a small portion of diseased 

 cotyledon on the center of the surface of the soil, others by placing bits 

 of mycelium from agar tubes in the same position. Within a few days 

 the mycelium could be seen plainly with the naked eye passing from both 

 into the soil and spreading over its surface. After four weeks it was iso- 

 lated from all points of the soil surface. After more than a year it could 

 still be isolated in pure culture. Microscopic examination of mycelium 

 from the soil showed the same characters that are previously described 

 for cultures and the same detached cells. 



Summary of the Saprophytic Stage in the Natural Life History. 

 From all that has preceded concerning this stage we may draw some 

 conclusions. 



1. The fungus lives naturally in the soil, especially where there is an 

 abundance of organic material. 



2. It derives sufficient nutrient materials from the soil to grow and 

 spread extensively during this stage. 



