78 PHYLOGENY 
are always, or usually, so placed. For instance, in Melam- 
psoridium betulinum the teleuto-sori almost invariably originate 
directly below the stomatal pore. The cause of this cannot be 
merely the need of oxygen for respiration, since it has been 
shown that the intercellular spaces of a leaf are all well supplied 
in that respect. Fig. 37 is drawn from the lower epidermis of 
a leaf of Betula alba in which teleuto-sori were just beginning 
to be produced. The same thing is true of the teleuto-sori of 
Melampsora Larici-epitea and other Melampsorae,and apparently 
even of Phragmidium. In others of the lower groups, Uredin- 
opsis, Milesina, etc., uredo-sori are equally so placed, both 
Fig. 37. Melampsoridium betulinum. a, young sori of teleutospores, 
viewed through the epidermis, showing how they originate beneath 
a stoma ; at the lower right-hand is a sorus with only two teleuto- 
spores, x 300; b, three young teleutospores, forming a similar 
sorus, seated on a common base, x 600. 
primary uredo-sori (which represent zecidia) and secondary. It 
can be justifiably inferred that this was the primitive position 
in which the female gametes and afterwards the other kinds of 
spore-sori were formed at the beginning: in Puccinia and its 
allies this position is no longer maintained. 
Since in the Ustilaginales (a comparatively non-progressive, 
if not degraded, group) there is only one kind of spore besides 
the basidiospore and the ensuing conidia, and this is produced 
irregularly and not in definite sori, it may be inferred that the 
same was true of the primitive Uredinales. This one kind of 
spore must have been the equivalent of the teleutospore. It is 
