334 Blackman . — On the Fertilization , Alternation of 
under water, and one of the four cells was putting out a germ-tube 1 . Inside 
the gelatinous mass of teleutospores access to free air must be difficult, and 
it is probably in such a situation that the promycelial cells tend to germinate 
directly. 
Such cases as these of Gymno sporangium and Phragmidium show that 
the real germmating unit is the promycelial cell , and that under certain 
conditions it can become a separate spore, put out a germ-tube and behave 
as a sporidium, and no doubt cause infection. When growing normally, 
however, in air the development of the germ-tube is arrested, and it becomes 
a mere sterigma, on the end of which the primary sporidium is developed. 
The primary sporidium thus appears to be merely the arrested and swollen 
germ-tube put out by the promycelial cell, just as the secondary sporidium is 
merely the arrested and swollen germ-tube of the primary sporidium. The 
sporidia are probably nothing more than special adaptations to the develop- 
ment of the promycelium in air ; in the absence of air such a development 
would be unnecessary, for there would be no chance of the wind-dispersal of 
the sporidia. The primary sporidium is thus really secondary in nature, 
and bears the same relation to the promycelial cell (the true primary spore) 
as does the so-called secondary sporidium to the first-formed one. 
It is evident that the formation of the so-called promycelial cells is 
really nothing more than the division of the contents of the teleutospore 
into four spores, which may separate as such, but usually remain united 
and form four secondary spores — the sporidia. As far as is known, the 
teleutospore is quite incapable of forming a mycelium ; it seems then time 
that the term promycelium should be dropped, and the process of develop- 
ment considered merely as one of spore-formation. 
That the later development of the teleutospore is really a process of 
spore-formation has been obscured not only by the formation of sporidia 
(really the secondary spores), but also by the fact that, owing to the thick- 
ness of the spore-wall, a process of germination is a necessary preliminary 
to division. In Coleosporium , however, where the teleutospores are thin- 
walled and develop in situ , there is no process of germination, but the 
spores become directly divided into four cells, which normally put out each 
a sterigma and form sporidia. Holden and Harper (23), however, in this 
genus have lately observed cases in which the divisions of the teleutospore 
rounded themselves off and became directly spores. In such cases, the 
teleutospore, its real nature no longer obscured either by the process of 
germination or by the formation of sporidia, is clearly seen to be a spore- 
mother-cell which undergoes a tetrad division to form four spores . 
1 A somewhat different interpretation was placed upon this case at the time, but a comparison 
with Gymnosporangium gives the clue to its real nature. Sapin-Trouffy (48) has described a case 
in P. Malvacearum in which submerged promycelial cells separate and put out germ-tubes, which 
become sterigmata (and bear sporidia) only if they reach the air. 
