62 I imiiKiiitii ill Cereals 



successful and the hybrids wore fertih'. This fact confirnis the peculiar 

 genetic place of A. strigi>.sii aumtigst other cultivated oats, which was 

 suggested by its fungal reaction. 



Finally, the isolated genetic position of A. strujusti is proved by 

 the fact, which we find recorded ( I I ), that it is also iniuume to smut 

 UstiUnjo tivemte, whereas the cultivated forms of ^1. sativa are usually 

 severely attacked by this fungus'. 



Some other examples might be given illustrating how, by the aid 

 of genetic knowledge, the differences of various cereals in their be- 

 haviour to fungi become clearer; and vice versa how fungal reaction 

 helps us to understand the genetic relation of plant forms. But the 

 complete enumeration of all these examples would be out of place in 

 this paper. 



One objection may be raised against the broad application of fungal 

 reaction for genetic purposes. 



This is the phenomenon of so-called " bridging species" — cases in 

 which the biologic form of a fungus, after living on certain of its host- 

 species ("bridges"), becomes capable of infecting a species, which it 

 cannot infect after living on its other host-species. Pole Evans also 

 showed with black rust of wheat 1\ gniminis, that very susceptible 

 F^ hybrids of immune and susceptible varieties may serve as a "bridge" 

 between susceptible and immune sorts. 



But against this, in the first place, there are only very few cases 

 known of existence of " bridging species-." In the case of fungi of 

 cereals, they are found oidy in Pttccinia gni minis forma sp. tntici and 

 not in P. glumurum, r. triticimi, P. simplex {2, 5). Furthermore, we 

 must not forget that the biologic forms of P. r/raiidnis an- relatively 

 weakly specialized fungi; for example, /br;/i(( sp. tntici, as has been 

 shown in different countries, can infect not only wheat but, more or 

 less, barley also^. 



' Morphologically A. slrhjusa is very like A. burbata Pott.; and Dr Trabut and 

 ThellunR account the latter as the progenitor form of the former species. It would be 

 very interesting, therefore, to know the fungal reaction of A. biirbatii. 



- "Bridging species" are found in P. Si/mphyti Bromvruiii ¥. Miill. (M. Ward and 

 Freeman), Erysiphe graminis D.C., living on ilrnmiis (E. Salmon), in P. iirdiiiinis forma 

 sp. tritici (Freeman and Johnson), and Si)liiier(itlii'C(i Hiiniiili on Ah-hciiiilki (Steincr). 



■' One of the conclusions to which Freeman and Johnson came after their numerous 

 experiments with biologic forms of P. yraminis is that "two biologic form.s may inhabit 

 the same cereal without being identical" (.5, p. 75). This statement, as also the fact, 

 well-known to mycologists, of the existence in Australia of a different race of P. firaminis 

 /. tritici, which cannot infect Berberis, and all that is known about the difference in 



