337 
Nuclear Divisions in the Rusts . 
As will be at once seen, all of the sexual fusions shown in Figs. 26-40 
involve the conjugation of two uninucleated cells, through a pore of greater 
or less width. Further, since these figures are all similarly oriented, i. e. 
with the upper part of each figure pointed upward toward the top of the 
plate as toward the epidermis of the host, it is obvious that the fusing cells, 
at least so far as one can judge from sections, may be placed in almost any 
position with respect to each other. For example, the cells may be placed 
side by side, in the same plane, in much the same position as they are 
figured by Christman (Figs. 26, 27, 35, 36, 39, and 40). Perhaps even more 
frequently, in my experience, one of the fusing cells appears to lie somewhat 
below the other, as in Figs. 26, 28-34, 37, and 38, some of which suggest the 
conditions which Blackman figures (see, e. g. his Figs. 66-70). 
Figs. 26-33 are all drawn from preparations of Triphragmium tihnariae « 
Fig. 26 represents a preparation in which two pairs of fusion-cells are shown 
side by side. Although at this stage in the development of the fungus 
sexual fusions may be found at many points along the diffuse sorus in the 
same section, one rarely meets with two such instances so near together, 
and at the same time properly oriented to serve for drawing. The boundaries 
of the cells below are lost in the mass of hyphae pushing up around them ; 
but the upper parts, showing the fusions, are quite clear. One nucleus from 
each pair is somewhat stretched out, apparently in the act of moving toward 
the other conjugating cell. In the instance at the left, however, the bud, 
which is put out after the fusion, is starting to grow in the opposite direction. 
One of the left pair in this case has a uninucleated cell above. Whether 
this is a ‘ sterile cell ’ or not, I am uncertain, since it stains quite darkly, 
and it does not appear to be in any way degenerating. In the other 
instance, however, at the right, the cell just under the epidermis is un- 
mistakably a sterile cell, since it shows the characteristic signs of degeneration, 
both in its cytoplasm and in its nucleus. It is interesting to note that in this 
latter pair of cells the one is placed much lower than the other, and, further, 
the lower cell does not appear to have cut off any sterile cell at its tip. 
In the other pair at the left, the two cells at the time of fusing apparently 
had grown up to about the same level. The unusually long conjugation 
tube connecting the latter pair is another feature of especial interest. 
In the next figure, 27, several interesting features are shown. In the 
first place, the conjugating cells are placed parallel to each other and at 
about the same level. Further, the right gamete has a degenerating sterile 
cell attached at its tip, whereas the left gamete has none. The point of 
contact of the two cells is apparently rather a small area ; hence the hole 
through which the fusion of the two protoplasts takes place is as yet compara- 
tively small. The left nucleus is clearly moving over into the right half of 
the fusion-cell, so that it actually appears to have pushed into and slightly 
indented the other nucleus. It is quite possible that Blackman would 
