482 
Journal of Agricultural Research 
Vol. XXVII, No. 7 
a, b, c, and d). It was not apparent that a single nucleus migrated to the 
tip of the promycelium and divided there, but division appeared to 
occur in the spore and in the elongating promycelium. 
As the sporidia developed, a single nucleus usually passed from the 
promycelium into each sporidium (fig. 2, e and f, and PI. 3, A). Oc¬ 
casionally all the nuclei were not utilized in this manner, for some of 
them remained in the promycelium. The subsequent history of these 
remaining nuclei was not followed in such cases, but it is possible that 
they may pass into outgrowths of the promycelium which have been 
observed to develop after the production of sporidia. 
The nuclei are small, approximately 1.6/4 in diameter. At times only 
the nucleolus, approximately 0.5/4 in diameter, was visible. 
When the sporidia germinate, the single nucleus divides. Mitotic 
figures were not observed, although segregation of chromatin elements 
was apparent in several instances (fig. 2, g). The origin of a binucleate 
condition of the germ tube often was apparent in the sporidium before 
the latter had been observed to germinate (fig. 2, h, i, j, and Pi. 3, B). 
As germination proceeded, these nuclei were observed to have further 
separated until they took up positions such as are indicated in 
fig. 2, k and 1 , and Plate 3, C. In the latter instance only two nuclei 
are visibly in focus in the germ tube of one sporidium (PI. 3, C, a); 
the other two nuclei appear as a dark band (PI. 3, C, b). The binucleate 
condition of the germ tube may persist for some time (fig. 2, k, 1, and 
m). These nuclei, however, apparently are only half the size of the 
original nucleus of the sporidium. Occasionally, also, germ tubes were 
observed in which four nuclei were present (one germ tube in fig. 2, m). 
When the sporidia conjugated, it appeared as if the single nucleus of 
each migrated into the fusion germ tube. This, however, occurred so 
rarely that the complete nuclear history could not always be followed. 
Sometimes in a single spore some sporidia conjugated and others ger¬ 
minated in the manner indicated above (fig. 2,0). Each process resulted 
in the production of a binucleate germ tube, although the origin of the 
nuclei was distinct in each instance. 
The process was not followed beyond the stages mentioned above. 
At no time, however, were the tips of the germ tubes observed to have 
become septate but remained unicellular. They characteristically 
contained two nuclei which most frequently were derived originally from 
the single nucleus of the sporidium. 
In a histological study of the tissues of seedlings which had been inocu¬ 
lated with germinating spores it was found that, after infection had 
occurred, the infection hyphae did not contain more than two nuclei. 
Although the sporidia are not abstricted from the promycelium, they 
characteristically contain a single nucleus at first. This nucleus has been 
observed to divide prior to the germination of the sporidium, so that the 
sporidium may contain two nuclei which have arisen in a manner com¬ 
parable to that in sporidia of many higher basidiomycetes. (Cf. list of 
number of nuclei in the cells of the Basidiomycetes, Levine, 27, p . 
164-170.) 
Also, the sporidia are definite structural units which germinate by 
means of a germ tube much smaller than the body from which it arises. 
Hence, it seems that they should still be considered as sporidia, although 
Paravicini (36) and others have suggested that homologous structures in 
other species of Urocystis should not be so considered. In some respects,. 
