70 Wisconsin Academy of Sciences, Arts, and Letters. 
region of contact the membrane remains intact. In Fig. 12 the 
fusion nucleus has not yet reached, the oval shape. The 
chromatin threads still maintain a quite uniform size. They 
seem to assume no particular direction but are somewhat 
massed along the zone of contact of the nuclei (Fig. 12). In 
this zone the threads seem to be slightly finer than those which 
are found in the other parts of the nucleus. It seemjs that the 
chromatin threads are also withdrawing from certain irregular 
areas of the nuclear cavities. Some of the threads appear 
much coarser than before, but they vary in diameter in differ¬ 
ent parts and are connected with each other and the nuclear 
membrane by still finer threads. The coarser threads are 
doubtless chromatin and the finer ones may represent the linin 
network. Uu to this time there is no apparent change in the 
nucleoli, either in their structure of position. In the next 
later stage which I found there is a single nucleolus. It seems 
entirely probable that the two nucleoles fuse. At a later stage 
the nucleus appears still more swollen and less completely 
filled with the chromatin thread. The threads tend also to be 
more massed together. Frequently the masses are so dense that 
the filaments are not recognizable as such. This stage (Fig. 
14) is probably one of fairly long duration and may corres¬ 
pond to the so called synapsis stage in the nuclei of the higher 
plants. At this stage no matter how deeply the surrounding 
cytoplasm may be stained the nuclear sap is perfectly trans¬ 
parent. While these nuclear changes have been going on the 
teleutospore has been increasing in size and this growth con¬ 
tinues till the promycelium is fully formed. The size of the 
teleutospore varies considerably and Fig. 3 represents one 
which is rather larger than the average. The resting fusion 
nucleus is nearly spherical and occupies a quite constant posi¬ 
tion near the center of the cell. The nucleolus in this and the 
following stages occupies a position near the periphery of the 
nucleus. The next change, which the fusion nucleus under¬ 
goes, consists in the loosening up of the denser chromatin 
masses. The threads become definite in outline and are more 
readily traced (Fig. 15). They increase in thickness and 
sharpness of outline. The increase in thickness is probably 
