1906] CURRENT LITERATURE 315 
Experiments with Hieracium.—OsTENFELD and ROSENBERG have under- 
taken a series of experimental and cytological studies of the species of Hieracium. 
RoseNBERG has published? a preliminary report of some of his results; but the 
first paper of the series has just been received. It is by OSTENFELD,’° reporting 
the results of castration and hybridization experiments. The castration experi- 
ments, carried on in 1903, 1904, and 1905, resulted in showing that in the genus 
Hieracium there are apogamous species, non-apogamous species, and transition 
species, and that the three subgenera conform in a general way to this division; 
Stenotheca having typical fertilization (the most primitive stage); Pilosella being 
intermediate, with both apogamous and non-apogamous species (the former in 
the majority); and Archieracium being entirely apogamous (except the H. 
umbellatum group). Attention is called to the fact that Taraxacum has “gone 
a little farther,” all its species being apogamous. 
The hybridization experiments are only in their inception, but the following 
results may be noted: a hybrid was produced between H. pilosella and H. 
aurantiacum, with greatly reduced fruiting power; H. excellens, itself probably 
a natural hybrid and producing only abortive pollen, gave hybrids by crossing 
with H. aurantiacum and H. pilosella; the hybrids arising from the same cross 
are heterogeneous; the fruiting power of hybrids is very slight.—J. M. C. 
Infection experiments with mildews.—REED*"* has added a further contribu- 
tion to the work inaugurated by NEGER and extended by Marcuat and SALMon, 
bearing on the transferability of physiological forms of the Erysipheae from one 
specific host to another within a closely related group of plants. The results 
in general confirm the conclusions of previous investigators; namely, that there 
exist races of E. graminis and other species of mildews which have become 
specifically adapted to a single species, or more rarely to several species of one 
genus of host plants. Reep finds, for example, that E. graminis from Poa 
pratensis will not infect other species of Poa except in some instances. Thus 
P. nemoralis is sometimes infected, while P. trivialis and P. compressa are infected 
very rarely. By this and other investigations the fact that a high degree of speciali- 
zation exists in the e Erysipheae, 2s in other groups of fungi, has been definitely 
established. While further demonstration of the existence of biological races 
is of less importance, the facts ascertained in this field of research furnish an 
excellent basis for other investigations, as for instance, the question of the per- 
manency of these races, the problems connected with abnormal predisposition of 
the host plants, and others, some of which have already received attention. 
-—H. Hasserprine. 
° Ber. Deutsch. Bot. Gesells. 24: 1906. 
7° OSTENFELD, C. H., Ex xperimental - se i studies in the Hieracia. 
I. Shinde and eons expermients with so sae aa of Hieracia. Bot. 
Tidssk. 27: 225-248. pl. 6. 
** REED, GEorGE M., esas experiments with Erysiphe graminis DC. Trans. 
Wis. Acad. Sci. 15:135-162. 1905. 
