CHAPTER V 
SPECIALISATION 
The Uredinales are strictly parasitic (obligate parasites). 
Many parasitic Fungi can live for a time saprophytically, but 
those belonging to the present group are quite incapable of 
such an existence. They are wholly dependent upon their 
host. Moreover, a study of the evolution of the Uredinales 
shows us that they have sprung from some simple beginning 
(resembling perhaps remotely the Ustilaginales) in such a way 
that new forms ever appeared as new hosts were evolved, and 
advanced part passu with them. The lowest forms are those 
parasitic upon the Ferns, the highest are among those on the 
Compositee and others of the more specialised orders. 
Each form is more or less closely adapted to its particular 
host, but there is a wide range among them in this respect. A 
species which can find sustenance upon hosts of more than one 
kind is called plurivorous. One of the widest is Puccinia 
Malvacearum, confined, indeed, to the Mallow family, but 
appearing to spread to nearly every genus of the group Malvex 
of that family. It has been experimentally shown that it can 
be transferred from Malva to Althaea and vice versd, and obser- 
vations on its occurrence in nature imply that it can pass 
equally to other genera (see under that species). Or a species 
may be found only on part of a subfamily, as P. Arenariae on 
many genera of the Alsinew. Others are confined to a single 
genus, but appear to be equally at home on almost any species 
belonging to it, as P. Violae. Still others are restricted so far 
as we know to a single species, as P. Buai, and various species 
