340 Blackman . — On the Fertilization , Alternation of 
to be observed in the fertile cell while the nucleus of the sterile cell above 
was still in position (Figs. 63 and 64). The disappearance of the nucleus of 
the sterile cell is doubtless to be accounted for by early disorganization, 
and the peculiar position in the fertile cell of the small nucleus by 
a change in position after migration, or by the fact of its having entered 
at the side. 
It would appear that the two nuclei of the fertile cell soon become similar 
in size and shape, for it is only occasionally that a dissimilarity can be 
observed. Very soon after this condition has been attained the fertile cell 
proceeds to elongate, pushing its way through the sterile cell (Fig. 61) and 
soon completely destroying it. The paired nuclei divide by the process 
which has been termed conjugate division, and the fertile cell cuts off 
a series of cells (aecidiospore-mother-cells), which do not develop directly 
into aecidiospores, but each cuts off a small cell below, known as the inter- 
calary cell (Figs. 71-74). It has been suggested that the function of this 
cell, which becomes disorganized and disappears soon after its formation, 
is to act as a disjunctive apparatus, and so bring about the complete 
separation of the aecidiospores. A mature aecidiospore is shown in Fig. 
75. Most of the fertile cells become binucleate and develop further, for 
in older stages of the aecidium only a few of the fertile cells are found, 
here and there, still uninucleate. It is no doubt these cells, which never 
achieve the binucleate condition, that are found crushed and distorted in 
still later stages h 
Although two is the usual number of nuclei in the fertile cell, the 
number three is nearly always to be found in one or two cells of each 
aecidium, and in one case it was found no less than four times in a single 
aecidium ; but in comparison with the normal number it is of course very 
uncommon. The three nuclei divide together by a process of conjugate 
division (Fig. 77), and trinucleate aecidiospore-mother-cells (Fig. 76) and 
aecidiospores are produced, the fate of which is unknown. In one case also 
a fertile cell with four nuclei was to be observed. 
How this multinucleate condition is brought about is not quite clear ; 
it may be due to the migration of more than one nucleus into the cell, or 
the division of one or both of the nuclei without cell-wall formation. In 
a fertile cell which was yet undivided one of the nuclei was observed to 
be apparently undergoing division while the other was in the resting state. 
When three or four nuclei were observed in an undivided fertile cell it was 
interesting to note that their size was usually considerably less than that of 
the normal paired nuclei. 
1 The fertile cells are often in contact with several of the cells of the tissue below, owing to the 
irregularity in length of the former, and the usually narrow form of the latter when they do not torm 
distinct basal cells ; a more than sufficient number of nuclei is thus at hand to supply all the 
fertile cells. 
