W. B. Grove. 
* 6 $ 
teleutospore which germinated basidially. Barclay’s account 
shows how this may well have arisen. Such a change would tend 
to an increased spread of the parasite, for the basidiospores are the 
most delicate possible of spore-forms and the mortality among them 
must be enormous. In some experiments which I have recently 
carried out in the open with Puccinia Cay ids (see Journ. Bot., 
1913, p. 42), it is quite within the mark to say that scarcely more, 
than one or two in a billion basidiospores achieved their end 
in infecting the Nettle. A spore which germinates like an ascidio- 
spore has many more chances of establishing itself upon its 
victim than one which produces basidiospores. 
From this to the intercalation of uredospores is but a small 
step. In some species secidiospores and uredospores are almost 
exactly alike in size and form. We know of cases where uredospores 
are few and rare; the steps to those instances where uredospores 
are numerous and form the chief means of fresh infection are 
many and abundantly represented. Such cases, which include 
many of the Puccinice on the Grasses, often belong to widely 
distributed species. One can even conceive of a state of things 
(largely perhaps dependent upon climate) where the fungus relies 
entirely upon uredospores for its existence, and loses altogether 
the other spore-forms, at first functionally and at last morpho¬ 
logically. The Black Rust of Wheat ( P . gratninis) in Australia and 
Uromyces Fabce in Ecuador seem to be approaching such a condition. 
So far the fungus is considered to be autoecious. The formation 
of the hetercecious habit demands, on this hypothesis, a sudden, 
but not inconceivable mutation, of which evidence will yet he found 
From the complete autoecious species, on the other hand, Brachy- 
and Micro-forms might easily arise by the dropping out of some 
of the spore-forms as occasion demanded. 
The reverse process of forming autoecious species with all 
spore-forms from those having only teleutospores of the type of 
P. FEgopodii (which has no spermogones), as imagined by Dietel 
in his second hypothesis, would imply the introduction of function¬ 
less gametes separately on each such occasion. The very persistence 
of the occurrence of the useless spermatia in so many species is 
a proof of their deep underlying primitiveness, and no hypothesis 
of the evolution of the higher Uredineae is tenable which does not 
start with the existence ot them and of the correlative female cells. 
The Botanical Laboratory, 
University of Birmingham. 
