ONION SMUT FUNGUS. 



129 



Observation of the exact course of events in the formation of a spore is 

 rendered difficult by the denseness of the mass of developing spores, and 

 b}' the fact that in the young stages all the developing parts stain so 

 deeply on account of their very active protoplasm that the nuclei and 

 septa can hardly be made out. In all cases which have been observed, 

 the spore begins as a lateral or terminal branch which curves back on itself 

 in the form of a crozier (Fig. 6, A-I). These hook-like croziers may be 

 seen in enormous numbers in the mycelial tangle at the initiation of sporo- 



FiG. 6. — Stagesof sporogenesis. A-P, development of the crozier and origin of theenvelop- 

 ing hyphap; Q, section through young spore which is shown in surface view at R; S, sec- 

 tion through mature spore. 



genesis. Even after the spores at the center of a sorus are fully formed, 

 one may still find various stages of development extending as far back as 

 the crozier, as he passes from the center toward the periphery of the tangle. 

 The croziers remind one of those from which the asci of the AscomA^cetes 

 are developed. They stain very deeply, and apparent!}^ the protoplasm 

 from the other cells of the hyphae passes into them. The various shapes 

 which they may assume are best understood by consulting Fig. 6. By 

 growth from the apex of the crozier a complete circle is soon formed and 

 then a spiral if further terminal elongation occurs (Fig. 6, F, L, N, P). 

 At about this time the crozier or spiral begins to appear angular and 



