338 Olive . — Sexual Cell Fusions and Vegetative 
maintain that this is a case of nuclear migration. At the same time, it is 
undoubtedly a case of cell fusion, and quite similar to those instances 
described by Christman in which conjugation has occurred between two cells 
lying side by side. 
In Fig. 28 the relation which the two fusing cells sustain to each other 
is somewhat uncertain. Although the lower cell appears to belong to the 
same hypha as the upper, I doubt that this is the correct interpretation, 
for careful focussing seems to show that the lower cell is from a distinct 
hypha which comes up obliquely toward the eye. It is important to note 
here again that the upper cell has attached to its tip, just under the 
epidermis of the host, a degenerating cell ; and also that the budding 
growth has begun even before the lower nucleus has passed over into the 
companion cell. Many similar instances to the one figured show that the 
bud generally pushes out to one side of the sterile cell, instead of crushing 
directly into the latter. 
Fig. 29 shows a much later development, in which the second bud has 
started off from the binucleated fusion cell. Even at this late stage, the 
interesting fact may be noted that two distinct cells enter into the composi- 
tion of the fusion cell, or basal cell. The two nuclei lie, however, in the 
upper gamete. The remnant of the old wall, which formerly separated the 
two gametes, and through which the conjugation took place, is very sharply 
brought out in the figure, although it has apparently been almost completely 
absorbed. The younger bud at the right is cut obliquely lengthwise at its 
tip ; hence its peculiar irregular shape, instead of the usual form with 
rounded end. An old dead sterile cell, not shown in the drawing, lies 
between the two buds. It probably once belonged to the upper of the two 
fused cells, but the rapid growth which followed the conjugation has dis- 
placed it from its original position. The larger bud in this case, although 
it has been cut off by a wall from the basal cell, does not yet constitute 
a spore, since a stalk will first be cut off below, to bear the oval spore at its 
tip. That the two nuclei of this bud are, in fact, in the prophases of conju- 
gate division is indicated by the vacuolated condition of the nucleoli, and by 
the appearance of the chromatin. The same is true for the two nuclei 
below, but neither pair is adapted to show the minuter details of the process. 
Still later stages, in which the binucleated basal cell has successively budded 
off, in the manner indicated in Fig. 29, several spores, each borne on a slender 
binucleated stalk, are abundant in the same preparation. The method of 
formation of the primary uredospores of Triphragmium , therefore, agrees 
exactly with that described by Christman (W 1 ) for Phragmidium poientillae- 
canadensis , thus adding further confirmatory evidence to Christman’s con- 
tention that the primary uredospores are morphologically equivalent to the 
catenulate aecidiospores. 
Figs. 30-33 show still further variations in the relative positions of the 
