124 FROMME: SEXUAL FUSIONS IN FLAX RUST 
it is borne. A later stage is shown in FIG. 20. The trinucleated 
spore at the top of the chain has cut off a small intercalary cell 
while the spore mother cell just below is as yet undivided. Fic. 21 
shows a mature aecidiospore which contains three nuclei. Such 
spores are frequently found lying free in the cavity under the 
epidermis among the ordinary binucleated type. A mature 
aecidiospore containing six nuclei was also found. See FIG. 22. 
This condition might have been brought about by the division 
of three original nuclei without the formation of the intercalary 
cell. 
Cell fusions between four gametes are sometimes found along 
with the two- and three-celled types but are relatively infrequent. 
I have observed only three well-defined cases of this nature. Two 
of these cases are shown in FIG. 23 and 24. The four cells that 
have participated in the fusion can be seen distinctly, but the 
cell contents were stained so strongly that the nuclei could not be 
distinguished. 
Still more striking are the large multinucleated spore mother 
cells which are occasionally found in the aecidium. One of these, 
FIG. 25, contains eleven nuclei. The cell is being divided by an 
ingrowing cell wall near the center. The uneven number of 
nuclei is probably due to the sectioning, but it is impossible to 
locate it with certainty on the next section. Another of these 
large structures is shown in FIG. 26. The evident pairing of the 
eight chromatin masses indicates that a division of four nuclei 
is just being completed. The base of the cell is indistinct and I 
am not able to determine its origin. Fic. 27 shows a case of a 
completed division of a four-nucleated cell forming a distinctly 
four-nucleated aecidiospore and an intercalary cell in which the 
nuclei are less distinct but evidently four in number. It seems 
quite probable that the conditions shown in FIG. 26 and 27 have 
resulted from an original four-cell fusion. Attention has been 
called to Olive’s observation of large multinucleated cells at the 
base of certain young aecidium cups especially in Puccinia Cirsit- 
lanceolati. He was inclined to interpret these as sporophytic 
structures resulting from the greatly stimulated growth following 
sexual fusions. Whether these are really central organs from : 
which the aecidium develops, has not been established. There #® 
