130 TECHNICAL BULLETIN 4. 



irregular (Fig. 6, M), due to protuberances which mark the origin of short 

 lateral outgrowths which soon curve inward along the surface of the devel- 

 oping ball (Fig. 6, P). The whole structure becomes so complicated at 

 this time that it is not always possible to make certain of the exact course 

 of events. The surface view now shows a dense ball of interwoven hyphae 

 (Fig. 6, R) . A cross section (Fig. 6, Q) shows that at the center there is a 

 larger cell which represents what will later be the fertile cell of the spore. 

 This cell appears to be the enlarged terminal cell of the crozier, though it is 

 not certain that this is always its origin. Also it is not entirel}^ certain that 

 all the branches which form the outside of the tangled mass arise directly 

 from the surface of the crozier. In some cases one gets the impression 

 that other hypha? may be involved, or that branches arise from below the 

 crozier on the same hypha. The transformation from the stage represented 

 in Fig. 6, Q, R, to the mature spore is very rapid. The central cell enlarges 

 while the cells of the surrounding hypha? become pressed tightly against 

 and united with it. The union between the central cell and the cells of 

 the enclosing hyphse appears to be stronger than that between the cells 

 of a single hypha of the latter; at any rate, the hyphse now break up and 

 their elements no longer appear as cells of individual hyphae, but as scat- 

 tered conical cells whose flattened bases are firmly attached to the surface 

 of the central cell (Fig. 6, I) . This involves a decided change in shape as 

 well as orientation. Nothing has been seen in this process which could 

 be called a gelatinization of cells, such as has been described so often as 

 occurring during sporogenesis in the Ustilaginales. 



Approximately at the center of the fertile cell of each fully developed 

 spore there is a nucleus which stains very prominently at this stage of 

 development (Fig. 6, S) . In thousands of beautifully stained spores exam- 

 ined by the writer, more than a single nucleus has never been found. It 

 is 3 to 4fx in diameter, with a prominent very red single nucleolus of about 

 .6// diameter, usually in contact with the nuclear membrane. The mem- 

 brane is very plain, but the nuclear content, with the exception of the 

 nucleolus, appears only as a few fine granules of cromatin aggregated about 

 the nucleolus or around the inside of the membrane. In each accessory 

 cell there is a single small nucleus of about the diameter of the nucleolus 

 of the fertile cell. In Urocystis Violae, Dangeard reported that there were 

 no nuclei in the accessory cells. With the staining methods used it was 

 impossible to determine whether the nucleus of the mature spore results 

 from the fusion of two nuclei. In U. Anemories (Pers.) Wint., Lutman 

 found that the cells of the vegetative hyphse are binucleate and remain 

 so until after the formation of the spore ball, and that the large nucleus 

 of the mature fertile cell results from fusion of the two nuclei. Such might 

 well be the case here, because in the vegetative hypha?, as previou^ly 

 mentioned, about half of the cells are binucleate, while in the mature 

 spores all cells are uninucleate. 



With the full development of the sorus, the host tissue above it dries 

 out and may split open and permit the escape of the dry powdery mass of 



