99 
The Evolution of the Higher Uredinece. 
and none at all on the Salicacese or the Coniferae, though Uredineae 
of lower type are frequent on those Orders. This shows that, as 
the more specialised orders of angiosperms arose in the course of 
evolution, fresh parasites of a higher type were evolved to suit 
them. 
Spore-Forms and their Relations. 
In speaking of the Micropuccinias so far, it has been assumed 
that the existence of species with one spore-form arose by sup¬ 
pression of the others. But reduction alone is never capable of 
providing a full explanation of the evolutionary process ; there must 
always have been an advance in complexity first. If we consider 
Schroter’s classification we see that the one spore-form which runs 
through the whole series is the teleutospore (including, of course, 
the basidiospore which is its invariable product); this is present in 
every case, whatever else may be absent. 1 It is natural to conclude 
that this is the essential and ancestral type of spore. 
But if the theory of Blackman and others that the secidium re¬ 
presents a remnant of a formerly existing sexual process is accepted, 
as it must be, then a spore produced like the aecidiospore must also 
be one of the ancestral types. 
Again, there are many grounds for assuming that the secidio- 
spores, uredospores, and teleutospores (and even the spermatia as 
well) are all modifications of one common spore-form. The for¬ 
mation of spermatia in the spermogone takes place much in the 
same way as that of secidiospores in the aecidium, except that there 
are no intercalary cells. In certain cases primary uredospores take 
the place of secidiospores, being followed by secondary uredospores, 
alike in form but differing in the character of the sorus, and 
probably in all such cases the primary uredospores alone are 
accompanied or preceded by spermogones, as in P. obtegens. Another 
species, P. Podophylli , has primary and secondary secidiospores, 
the latter taking the place and function of uredospores. In 
Uromyces Veratri similar spores, if sown upon young leaves 
produced only uredospores; if on old or sickly leaves produced 
more teleutospores (18). It is well-known that teleutospores are 
commonly borne upon the same mycelium as uredospores; but also 
secidiospores can^be followed by teleutospores upon the same 
1 Isolated “ species” of Uredo and ^Ecidium are ignored, because there 
is reason to believe that all, or nearly all, of these will be assigned to other 
species as our knowledge of them increases. Of the 38 “ imperfect species ” 
recorded in Plowright’s Uredineae, only four are now still unassigned. 
