1919] CURRENT LITERATURE 181 



among various fungi. Some 68 species of fungi, the majority of them belonging 

 to the Uredinales, have been reported to show such specialization. The first 

 known and best studied species is Puccinia graminis, producing the destructive 

 stem rust of wheat and of other cereals and grasses. A few species having a 

 wide range of hosts, like P. subnitens, appear not to be specialized. The cita- 

 tion of literature includes 174 titles, supplied by 67 writers, indicating the 

 prominence which this line of investigation has attained within the last few 

 years. Eriksson's studies on the specialization of the grain rusts, reported in 

 1894, introduced the subject, but the fixed and unchanging character of physio- 

 logical strains has first been shown definitely in the present paper, since being 

 confirmed by Stakman and others.^" 



It is pointed out that so far the data do not indicate that bridging species 

 are capable of altering the physiological nature of the parasite so as to enable 

 it to extend the range of its natural hosts, as has heretofore been assumed. In 

 fact, it appears that among fungous parasites there are definite strains or races 

 not distinguishable morphologically, but only by their physiological behavior 

 in infecting certain hosts, and that these strains retain the same characters 

 through all the metamorphoses of the fungus, and when tested by use of any 

 kind of reproductive body that the particular species produces. The specializa- 

 tion of the same fungus in widely separated regions may possibly be different, 

 but the data are scanty. The relation of physiological specialization to mor- 

 phological variation is barely mentioned. The whole subject of specialization 

 is one of great scientific and economic interest, making the present admirable 

 summary particularly timely. — ^J. C. Arthur. 



Heath and grassland. — Continuing the investigations already noted" of 

 certain English heaths and grassland. Farrow" has accumulated more data 

 upon the eflfects of a rabbit population upon vegetation retrogression. It is 

 demonstrated that the presence of rabbits alone is sufficient at times to change 

 a pine forest through Calluiia heath and Carex arenaria associations to a dwarf 

 grass or a Cladonia heath. Experiments with irrigation and with the applica- 

 tion of manure tend to show that both sterile soil and lack of soil moisture 

 are factors in limiting the rate of growth and the luxuriance of the vegetation. 

 This increased growth with imt)roved conditions results in a decrease in the 

 number of species in the area, since the more rapid growth of certain plants, 

 like Agrostis vulgaris, smothered less vigorous ones, such as Festuca ovina. 



20 Stakman, E. C, Parker, J. H., and Piemeisel, F. J.. Can biologic forms of 

 stem rust on wheat change rapidly enough to interfere with breeding for rust resist- 

 ance? Jour. Agric. Res. 14:111-123. ph. 13-17. 1918. 



^' BoT. Gaz. 64:263. 1917. 



" Farrow, E. P., On the ecology of the vegetation of Breckland. III. General 

 effects of rabbits on the vegetation. IV. Experiments mainly relating to the available 

 water supply. V. Observations relating to competition between plants. Jour. 

 Ecology 5:1-18, 104-112, 155-172. 191 7. 



