Lictman—Life History and Cytology of the Smuts. 1209' 
but this is exceptional. Each cell of the promycelium is uninu- 
cleated. If now some of the promycelia be taken from the 
cultures 3-5 days old it will be seen that conditions are chang¬ 
ing. The cytoplasm of each cell of the fused pair is becoming 
highly vacuolated and the nucleus of one cell can be found at all 
stages of passage from one over into the other. This passage 
of the nucleus can be traced in great detail from one cell into the 
other (Figs. 30-32) through the conjugation tube. In the pas¬ 
sage it often becomes drawn out or amoeboid in shape. This 
movement of the nucleus occurs before there is any flow of cyto¬ 
plasm ; seeming to be the result of some kind of an attractive 
stimulus exerted on one nucleus by the other. It is probable too 
that food supply has something to do with it as the movement 
seems to be toward the better nourished cell. The cytoplasm of 
the enucleated cell becomes more and more vacuolated and the 
material in it begins to withdraw into the one with the two 
nuclei (Fig. 33). As it retreats from the enucleated cell it 
builds successive walls behind it (Fig. 34). The enucleated 
cell finally appears very much shriveled as a result of losing its 
contents and in some cases with a number of cross-walls marking 
the successive retreats of the cytoplasm. In the last stage all 
the material from both cells is found in the one with the two 
nuclei. The two nuclei may now lie side by side closely pressed 
together or they may be at some distance apart. As to whether 
they actually fuse or not is rather difficult to decide but at any 
rate they become so closely pressed together that it is impossible 
to differentiate them as two in some cases (Figs. 33 and 34). 
It must be remembered too that at this time the cell is filled with 
large vacuoles in many cases and the nuclei are compressed be¬ 
tween them so as to lose their shape. At this stage, the nucle- 
ole, which earlier is easily differentiated, cannot be readily dis¬ 
tinguished. If the nuclear fusion occurs it is probably only in 
a part of the cases; in many, the two nuclei simply seem to lie 
separate in the cell until it dies. 
In one case (Fig. 35) that was observed, three promycelial 
cells had fused and the nuclei of all three was in the middle one. 
Another interesting variation is that which occurs sometimes in 
U. Avenae where a long fusion tube is frequently formed, the 
