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FRANK DUNN KERN 
Both short- and long-cycle forms agree in the gametophytic genera- 
tion which is initiated by the reducing germination of the teliospore 
and ended by a doubling conjugation previous to the production of 
the first spore-structure (the pycnia being disregarded). In the short- 
cycle condition the first spore-structure is another telial stage hence 
the sporophyte is represented only by the teliospores themselves and 
a small amount of growth accessory to their production. In the 
long-cycle condition the first spore-structure following the conjugation 
may be known as the aecial stage without regard to its form or struc- 
ture. In all cases the aeciospores give rise to a plant body (mycelium) 
which is sporophytic. In some forms it produces repeating spores, 
either like or unlike the aeciospores, but ultimately forms the telial 
stage, the end of the sporophytic phase. In heteroecious forms the 
two phases are produced upon the unlike hosts. Reasoning by analogy 
we are justified in regarding the gametophyte as the primitive genera- 
tion and it would seem to follow that the forms with the least developed 
sporophyte should be nearest the ancestral conditions. By a progres- 
sive development of the sporophyte, a prolongation of the double 
nucleated phase, we have an evolution which is comparable with the 
course of development of the higher plants. Some investigators have 
become so confident that this is a reasonable presumption that they 
have ceased to argue this phase of the problem but have gone on to 
discuss the origin of heteroecism, how the jump from autoecism to a 
new host could have come about, and which was the original gameto- 
phytic host and which the secondary one. 
If the rusts have made such advances in their sporophytic genera- 
tion we have a condition which may force us to modify our ideas of 
parasitism. The whole question is inseparably connected with the 
large problem of the genetic relationship of parasites. The question 
whether this group with all its complexity conforms to the nature and 
development of other parasites or stands as an exception is one which 
interests us today. 
Those who have regarded the rusts, in spite of their complexity, 
as a degenerate group of parasites also have advanced theories as 
to the probable course of development. It may be idle to speculate 
further with such theories but perhaps another viewpoint may permit 
new relations to be perceived. According to one view pleomorphy 
and even heteroecism are held to be the primitive condition and the 
autoecious short-cycle forms are regarded as the latest in evolution 
