E. V. Wulff —98— Historical Plant Geography 



The possibility of the utilization of the described biological peculiar- 

 ities of rust fungi for purposes of historical plant geography may be 

 illustrated by the following examples: 



Microcyclic forms of rust fungi may arise from heteroecious forms, 

 when in any country or region— as a result of a change in clirnate {e.g., 

 from temperate to cold or vice versa, from humid to arid or vice versa) 

 —their primary hosts, on which the aecia develop, die out, but their 

 secondary hosts, on which the generations of uredospores and telio- 

 spores develop, survive. In such cases the fungi multiply by means of 

 the uredospores (these generations can also winter over); the telio- 

 spores, however, at first are preserved in a rudimentary state (due to 

 the dying out of the primary hosts, they lose all their significance), and 

 then completely disappear. In this way there arise microcyclic forms 

 that cannot convert themselves into macrocyclic forms, even if in the 

 given locality their primary hosts should again make their appearance. 

 In western Europe, for instance, the rust fungus Cronartium quercium 

 propagates itself on oaks only by their uredospores, the teliospores 

 having completely disappeared, but in North America and Japan the 

 same fungus passes through a complete cycle, the aecia developing, 

 moreover, on two-leaved pines. It seems that in Tertiary times there 

 existed in Europe at least two species of pine resembling the North 

 American species on which aecia of Cronartium quercium are formed— 

 Pinus rigios (Oligocene-Miocene) , similar to P. Taeda, and P. hepios 

 (Oligocene-Pliocene), similar to P. mitis. Or let us take Tkecospora 

 vacciniorum. This rust fungus propagates itself on Vaccinium Myrlillus 

 and V. Vitis-idaea only by uredospores (teliospores are rare), but in 

 North America the same fungus passes through a complete cycle, the 

 aecia being formed on Tsiiga canadensis. But in the Pliocene period in 

 Europe there existed Tsuga europaea, which might well have been the 

 primary host of Thecospora vacciniorum. In the European part of the 

 U.S.S.R., in connection with the disappearance of the fir {Ahies) and 

 the larch {Larix) that had existed here in interglacial times, there arose 

 a considerable number of microcyclic Melampsoraceae. 



Sometimes macrocyclic and microcyclic forms are found side by 

 side, e.g., of Puccinia graminis in Great Britain. The microcyclic form 

 (only uredospores on cereals) could have arisen only in the following 

 manner: The host, the barberry (Berberis vulgaris), which existed there 

 in pre-glacial times, disappeared during the Ice Age, and there arose a 

 microcycUc form (minus teUospores). Later, however, when in Great 

 Britain the barberry again made its appearance (believed by some to 

 have been introduced by man), there reappeared with it the macro- 

 cyclic form of Puccinia graminis. These examples show that micro- 

 cyclic forms of fungi may give us a clue as to which plants (the 

 primary hosts of the fungi) died out in a given region due to cli- 

 matic changes that occurred there in former times. 



Very interesting data are presented by Lashchevskaya (1927), who 

 investigated the rust fungus that occurs on the Tertiary relic, Schi- 

 vereckia podolica, growing in a part of Kursk Region characterized by a 

 number of such relics. It was found that this rust fungus is Puccinia 

 drabae, a species of an exclusively mountain or north arctic-alpine type. 

 The hosts of this fungus are ordinarily several species of the genus 



