686 THE AMERICAN NATURALIST. (VoL. XXXII. 
tant significance, not only in this but in other orders of fungi 
where it occurs, there are reasons for not regarding the union 
in this case as representing true sexuality. On the other hand, 
although no one has as yet quite proved it, there appear to be 
reasons for supposing that, in the æcidial stage, a form of true 
sexuality occurs, comparable with what is known in some 
ascomycetous fungi. Time alone will show whether this pres- 
ent probability is a reality, but at any rate the position of 
Uredinacez in regard to sexuality is undoubtedly very different 
from that of bacteria and Saccharomycetes. 
One who takes up the recent descriptive works on Uredi- 
naceæ is surprised to see the number of species which depend. 
on physiological characters. The former method of describing 
the species of this order from the morphological characters of 
the teleutosporic, the uredosporic, and zcidial stages, was cer- 
tainly sufficiently perplexing, but one almost gives up in despair 
on seeing species in which the different stages are identical in 
all respects, except that some of them, usually the zcidia, will 
grow only on certain hosts. Facts like this are of course only 
determined by artificial inoculations, although they may some- 
times be suspected by the distribution of the different stages 
in nature. In this complicated state of things, more compli- 
cated than in any other order of plants, we are compelled to 
examine very critically the accounts of cultures made even by 
botanists of high reputation, and it is only natural that we 
should hesitate to give implicit confidence to negative results 
unless the observations have been repeated by other observers 
at other times and places. Even from scattered positive results 
one should avoid drawing too wide general conclusions. We 
may readily believe that some of the supposed distinctions in 
the choice of their hosts by different Uredinacez will be proved 
hereafter not to be founded in fact, but, making all proper 
allowances for possible errors in observations and for hasty 
speculation in a field where speculation is so easy, and accurate 
experiment so difficult, we have to admit that in a good many 
cases surprising results have been confirmed by repeated obser- 
vations, and the tendency to split up species on physiological 
grounds becomes more and more marked. 
