Nuclear Phenomena in the Smuts. 
485 
be distinguished when the process is complete, except for a 
slight enlargement of the tube diameter. The tubes may be 
long or short according as the conidia are more or less widely 
separated in the culture. They may be either straight or 
curved as in Fig. 18. Cells that do not become connected thus 
in pairs remain small, and their protoplasm frequently under¬ 
goes changes which cause it to stain as a homogeneous mass. 
The behavior of the promycelia which have been carried along 
in the cultures and have continued to bud is also noteworthy. 
The distal of the three cells of the promycelium is generally the 
smaller. When starvation intervenes the proximal larger pair 
of cells put out tubes from their adjacent ends which fuse and 
connect the two in the same fashion as the conidial pairs are 
connected. The fused pair now also enlarge greatly and their 
adjacent ends become rounded out by increased turgor. The 
cell wall splits and the two cells become free from each other 
except for the fusion tube (Fig. 19). In this condition they 
frequently become inclined at an angle to each other. Whether 
this change in their relative positions is due to special tensions 
in the walls of the fusion tube itself, or merely to chance as 
they float in the culture medium, is not easy to say. The distal 
cell is thus left unpaired, and much more generally than is the 
case with the similarly situated conidia, it undergoes a speedy 
disorganization. Its protoplasmic contents are aggregated in 
deep staining masses (Fig. 19), and ultimately the wall collapses. 
In some cases, however, where a conidium is lying near such a 
promycelium the distal promycelial cell forms a fusion tube 
with the conidium, and thus provided the pair enlarge and con¬ 
tinue in as thriving a condition as the two lower cells (Fig. 20). 
The resemblance of this whole process of cell fusion to a sex¬ 
ual conjugation is apparent. Externally it is like what hap¬ 
pens in the formation of a zygospore from the contents of two 
Spirogyra cells. There is, however, here no migration of pro¬ 
toplasm from one cell to the other, and what is still more sig¬ 
nificant, no fusion of nuclei. The nuclei remain in their respec¬ 
tive cells throughout the entire process without division or visi¬ 
ble interchange of nuclear substance. It appears like sexual 
fusion but no fertilized egg in the ordinary sense of the term is 
