126 FRANK DUNN KERN 
any bearing it points toward the short-cycle autoecious type as the 
most recent for here the pycnia may be omitted although in ontogeny 
there elapses a time for their development. 
In a parasitic group where there is such a close relation between 
parasite and host we might gain some idea of genetic relationship 
from a study of the distribution of the different types of rusts upon the 
series of hosts. Although the phylogeny of the hosts may not be 
regarded as settled the arrangement will permit this sort of a general 
comparison. It seems logical to assume that the lowest hosts would be 
parasitized by the more primitive forms while the higher host orders 
would be expected to have upon them the more advanced types. As 
already indicated we recognize but three types of parasites, heteroe- 
cious long-cycle, autoecious long-cycle, and autoecious short-cycle. 
The ferns are the lowest hosts for these parasites and their forms are 
pleomorphic and heteroecious. In order to have some numbers 
available a careful survey of North American forms having a definite 
known life-cycle has been made. Out of fifty species on Coniferales 
forty-seven are heteroecious. Glumaceous rusts are heteroecious with 
a single possible exception. In the Lily order while only seven are 
heteroecious, twenty-three are autoecious long-cycle forms, with a 
single short-cycle form. The Ranales have the three types almost 
equally distributed. In the large rose order the long-cycle forms 
greatly predominate but autoecism is three times more prevalent than 
heteroecism. Upon the final great aUiance, Campanulales, we find 
heteroecious phases but so far as present known life-cycles are con- 
cerned they are only half as numerous as short-cycle forms, the figures 
being thirty-two and sixty. If we make comparisons within the short- 
cycle series we find that they are almost unknown upon the lower 
orders whereas sixty out of a total of one hundred forty-eight known 
forms are found upon the highest order. If this sort of evidence is 
competent its indication is certainly plain. 
In a recent paper Olive has taken it for granted that autoecism is 
the original condition and has brought forward arguments bearing on 
the question as to which, of the heteroecious hosts is the primary one. 
With his premises as a basis he comes to the very logical conclusion that 
the present aecial host was the original host of the hypothetical autoe- 
cious ancestor. Part of the argument is that the gametophytic gener- 
ation being the more primitive should be on the primary host. To 
evolve the heteroecious condition the gametophyte has remained un- 
