NOMAD KUNGI. 115 



Microscopic Fungi will remember that he devotes a chapter to the 

 exposition of this theory of Dimorphism, and in his Handbook the 

 theory is practically followed up by the arraui^ement of the various 

 forms of Uredo with the species of Puccinia to which they belong, so 

 far as that was known. It is true that Cooke calls most of these 

 Uredos Tnchahmiis:, and professes to distinguish between the two 

 genera by assi<^ningto the spores of the latter the possession of afoot- 

 stalk, while the spores of Uredo, he says, " have no foot-stalk at any 

 stage of their existence." In fact, in the generic character of Uredo 

 he seems to assert that the spores of Uredo are developed by a kind 

 of segi-egatiou of the contents of certain hyphal cells, that is, bj' free 

 cell-formation. But this is untrue, unless Professor De Bary be totally 

 mistaken. The spores of Uredo are formed by constriction from the 

 end of a hyphal filament, which, when thus engaged, is called a 

 banidium. There is no difference between Uredo and Trichobasis, 

 except that in the latter case, in a few instances, a small fragment 

 of the basidium remains attached to the spore. 



But while the Dimorphism of these fungi was admitted, the fact 

 which still remained behind, namely their Trimorphism, was as yet 

 undiscovered. If the case had been with all the Uredineae as with 

 those which I have mentioned above, no doubt the fact would soon 

 have forced itself upon the mind. No one could long contemplate the 

 orderly procession of the three forms on tha same plant without being 

 compelled to acknowledge the probability of their genetic connection. 

 But, unfortunately for the mycologists of the past, the case was l)y 

 no means so simple. Many species of CEcidium were, and still are, 

 known which are not succeeded by a Uredo or a Puccinia on the same 

 plant. Many Ui-edos were, and a few still are alone, unaccompanied 

 by either an fficidium or Puccinia ; while there is a considerable 

 number of species of Puccinia with which no CEcidium or Uredo was 

 or is even now known to be associated. Still another fact complicated 

 the matter. Allowing that a Puccinia is preceded by an CEcidium, it 

 seems that we must not always look for the CEcidium upon the same 

 or even upon an allicl plant. Sometimes we shall find the CEcidium 

 upon a Dicotyledon, while the Uredo and Puccinia luxuriate upon a 

 Monocotyledon. This, which is known as hetercecism, is a curious fact, 

 and is especially the case with those species such as Puccinia pramiiiis, 

 P. corontita, P. poaruin, P. magiiusiana, and P. caricig, which grow upon 

 grasses and sedges in their final stage. These are called hetprceciouif 

 species, and their CEcidia are found respectively upon Berberis, 

 Rhamnus, Tussilago, Rumex, and Urtica. 



Life-History of a Heter(ecious Species. 



It will illustrate this important phenomenon of hetercecism, as well 

 as confirm the whole theory, if I trace the annual cycle of Puccinia 

 graminis through its various forms; for, if it is once proved that P. 

 graminis is descended from (Ecidinm berberidis. no one can any longer 



