402 Dastur . — Cytology of Tilletia Tritici , ( Bjerk . ) Wint. 
The sporidia are at first in direct continuity with the promycelium 
(PL XX, Figs, i, 8, and 9) ; the sporidium is cut off from the promycelium 
by a septum only after the nucleus has passed into the sporidium (PL XX, 
Fig. 27). The contents of the sporidia are at first dense, granular, and 
homogeneous ; at this stage the sporidia are invariably without nuclei, but 
later they become vacuolated, and only then does the migration of the nuclei 
from the promycelium take place. 
The sporidia are generally eight, but it is not unusual to find a larger 
or smaller number ; four to sixteen have been observed. It sometimes 
happens that a promycelium has more nuclei than sporidia, or more sporidia 
than nuclei ; what is the ultimate fate of the surplus nuclei and sporidia is 
not known. The sporidia are not always uninucleate ; occasionally they 
are binucleate (PL XX, Fig. 17), but more than two nuclei have never been 
observed. In Fig. 39 of Plate XX the right-hand sporidium has two nuclei. 
These two nuclei may have passed into the sporidium directly from the 
promycelium, or the nucleus from the central sporidium may have crossed 
over into the other sporidium through its unseptate base. 
Dangeard 1 has observed that the nucleus, during its migration into 
the sporidium, is at first elongate till it reaches the middle of the sporidium, 
when it becomes globular. But it is not unusual to find an elongated 
nucleus in the middle of the sporidium and a rounded one at the base. As 
a rule the nucleus is found in the lower half of the unconjugated sporidium, 
seldom in the upper half. Whether this has any physiological significance 
it is difficult to say. 
The conjugation of the sporidia takes place when they are still attached 
to the promycelium or after they fall off. As a rule the sporidia are linked 
by means of a single short conjugating tube ; but at times a pair are joined 
by two such tubes. The conjugation in most cases is between two sporidia, 
but on rare occasions there is a triple conjugation between the sporidia ; 
what happens to the third nucleus has not been observed. The nuclei of 
the conjugated pair proceed towards the connecting bridge and then the 
nucleus from one sporidium passes into the other (PL XX, Fig. 13). It is 
interesting that the nuclei in both the sporidia are generally at the same 
level in the two cells as they migrate towards the bridge (PL XX, Fig. 14). 
As the nucleus passes through the bridge it becomes elongated. Not only 
is there a passage of the nucleus from one sporidium into the other, but of 
the whole or part of the cytoplasm as well. After the cytoplasm has with- 
drawn from the upper and lower ends of the sporidium, septa appear at the 
free surfaces ; the empty or half-empty sporidium ultimately shrivels up. 
From the sporidium with the two nuclei and extra cytoplasm a germ-tube 
is given out, at the top of which a secondary sporidium is developed. It 
very easily falls off from its stalk. It can be readily distinguished from the 
ll 
1 Dangeard, P. A. : loc. cit., p. 2 66 . 
