344 Blackman. — On the Fertilization, Alternation of 
nucleoli remain for a time without fusion (Fig. 87 b ), as described by Sapin- 
Trouffy. In the next stage the nucleus has increased somewhat in size, 
the two nucleoli have been replaced by one large one, and the chromatin, 
which has hitherto not been well marked, begins to stain more deeply 
(Fig. 87 c ). The nucleus still increases in size, and the chromatin becomes 
resolved into a very well-defined thread which is apparently a single 
spireme (Fig. 88 a). This, however, is not the precursor of division, for the 
nucleus still increases in size and the chromatin returns to the condition of 
a fine network with the nucleolus as a somewhat elongated body flattened 
against the nuclear membrane (Fig. 88 b). The nucleus then goes into the 
resting state, in which it passes the winter, appearing as an almost homo- 
geneous body except for the well-marked nucleolus (Fig. 2). The process of 
increase in size and of formation of a spireme thread seems to correspond 
with the changes included under the term synapsis in the higher plants and 
animals, but it is not followed by nuclear division but by a period of rest in 
which the spireme again disappears. A somewhat similar case has been 
described by Williams (60) for the tetraspore-mother-cell of Dictyota , where 
after synapsis a similar disappearance of the spireme thread and a period 
of rest was found to occur. 
Gymnosporangium clavariaeforme. 
The perennial mycelium which inhabits the stems of Juniperus and 
bears in spring the yellow masses of teleutospores shows very clearly the 
paired nuclei in the cells of hyphae, which are thick-walled as described 
by Sapin-Troufify and others. As in the case of the teleutospores and 
uredospores of Phrag. violaceum , the teleutospores of this form are not borne 
directly on the mycelium but arise from comparatively large rectangular 
cells, which form a close-set layer on the surface of the mycelium, 
at the points where the teleutospores are developed. These each 
contain two nuclei which are somewhat larger than those of the ordinary 
cells of the mycelium, and show each a well-marked nucleolus (Fig. 89). 
They are similar to the teleutospore-bearing cells described by Sapin- 
Trouffy for G. Sabinae , but their side and lower walls are of considerable 
thickness. Each of these cells gives origin to a number (not more than 
three or four) of narrow outgrowths which develop into the stalked, two- 
celled teleutospores (Fig. 89). The outgrowths have paired nuclei (Fig. 90) 
and soon undergo two divisions, the first cutting off the stalk-cell, while 
the second divides the upper cell into the two cells of the teleutospore. 
The teleutospore then increases in size, the wall becomes thickened, 
and the cytoplasm vacuolar and filled with yellow, oily reserve-material. 
The two nuclei in the teleutospore fuse, earlier than in Phragmidium, 
before the spore has obtained its full size or thickness of wall. The wall 
