128 
FRANK DUNN KERN 
fusion, there should be produced at once teliospores instead of an inter- 
calation of one or more polymorphic spore-stages, the proper con- 
ditions for a short-cycle autoecious form would be at once established. 
In heteroecious forms only the reduced basidiospores following telio-''^ 
spore germination can infect the aecial host. In the abbreviated con- \ 
dition just outlined we have the necessary requirements for reinfection '.* 
and maintenance of a short-cycle telial form on what was the original- 
aecial host. Believing that the only fundamental stages are those of 
sexual fusion and teliospore formation neither is disturbed by such a 
shortening process. Teliospore formation which was an inherent 
capacity simply takes place sooner than formerly without the inter- 
vention of a somatic stage of such extent between sexual fusion and 
reduction. If teliospore production is to take the place of the former 
aeciospore formation there might be two expectations concerning their 
nature. They might be exactly like the former teliospores in which 
case nothing happens except the pulling of the stage backward to the 
other host, or they might be expected to have the morphology of the 
aecidiospores but behave physiologically like teliospores. The so- 
called genus Endophyllum fits the latter hypothesis and may have arisen 
in some such manner. The cases cited and numerous others fit the 
former. Such a theory does not fit badly with the present distribution 
of the types of rusts upon the phylogenetic series of host plants. Re- 
calling the fact that the tendency for heteroecious species is to have the 
gametophytic hosts higher in classification than the telial hosts we must 
expect the short-cycle forms which are to occupy the former gameto- 
phytic hosts to show an upward movement which would result in their 
occupation of the higher orders. I have already shown that is in 
accord with the facts based upon a survey of North American forms. 
Although it may be objected that these considerations do not explain 
the real origin of the group it may be claimed that they do express a 
trend of evolution, since a time when the group attained a parasitic 
mode of life, which accords with the course of development everywhere 
bound up with parasitic adaptations. 
Someone has said that nature produces individuals while man has 
created species. This seems hardly a proper observation for higher 
plants and animals but it applies well to the lower parasites. The 
fact that we hear of ''physiological" species, "biologic" races, and 
"formae specialis," in parasites is but an admission that man is the 
inventor of "species" of some groups and in order not to be misinter- 
