NOTES OX RECENT RESEARCH. 



697 



on Elymus arenarius. On the other hand, the uredospores — of the same 

 Puccinia — growing on Dactylis will attack Oats but not Rye, and similarly 

 in other cases." 



One of the interesting ideas which arose out of these results was 

 " that the different specialised forms — which, though not morphologically 

 distinct, are physiologically different from one another — are incipient 

 species ; that the particular specialised race adapted to grow on Wheat, but 

 not on Rye or Barley, is in course of becoming a species, and may daring 

 the lapse of time actually become a species of Puccinia, which will even- 

 tually show morphological differences in addition to the physiological ones it 

 already shows. Various names have been proposed for these physio- 

 logically but as yet not morphologically different varieties of the Puccinia 

 ijraminis. Eriksson termed them 'special forms' (forma speciales), 

 Rostrup names them ' biological species ' (biologiscJie Arten), Schroeter 

 chose the term species sorores, and Magnus calls them adapted races 

 (Gewohnlieitstrassen). . . . It is, of course, a matter of pure hypothesis as 

 to whether these intangible physiological differences will ever bring about 

 morphological changes of so obvious and relatively permanent a nature 

 that we should then recognise the differences as specific." 



The author gives an account of the Rusts that are found on the Bromes 

 and also a descriptive account of the species of Bromus used in the experi- 

 ments, all carried on with Puccinia dispcrsa. It should be mentioned 

 here for clearness that this Rust has its physiological forms, which are 

 adapted to species or groups, in a similar way to the case of Puccinia 

 graminis, and that the main object of these extensive investigations was 

 to find out what the various factors might be, in host or parasite, which 

 governs infection, and so the association of the several physiological forms 

 with particular kinds of Bromus. The numerous experiments themselves, 

 though of great interest and importance, must necessarily, on considera- 

 tions of space, be almost entirely passed over. Valuable ones, among 

 others, were undertaken on the germination of uredospores, the conditions 

 attending which had been astonishingly little attended to. It appears to 

 have been generally taken for granted that uredospores would germinate at 

 almost any summer temperature ; but this is not the case, the minimum 

 required being about 10-12° C. (50-53° F.), the maximum limit being not 

 far from 26-27"5° C. (78-81*5° F.), while the optimum temperature is about 

 20° C. (68 c F.). New light is thrown on some of Eriksson's results by 

 cardinal points here brought forward. Elsewhere it is interesting to note 

 that the author finds no evidence to support the remarkable hypothesis of 

 Eriksson, that at certain seasons the Rust fungus attacks the Grass — e.g. 

 AVheat — and passes the protoplasm of its spores into the embryo or some 

 other part of the plant, where it mingles with the protoplasm of its host 

 and lives a common life of symbiosis with the living cell contents, to break 

 out suddenly at a favourable opportunity as Rust. The last chapter is in 

 answer to its heading, " Is there any relation between infection and the 

 visible structural features ? " The answer given to this important question 

 may perhaps be sufficiently shown as follows : — " Or, again, spores from 

 B. sterilis readily infect B. madritensis, which has larger but fewer stomata 

 than the former species. How is it that B. maximus is almost immune 

 to these spores, although its stomata are far larger ? Is it because they 



