180 Referate. 



parent; that the Fj hybrid was, in fact, a bridging host. It was to test 

 the validity of this notion of a bridging host that the above experiments 

 were designed. The authors worked with P. graminü triticicompacti and the 

 cereals used were Haynes Bluestem \Mieat. Manchuria Barley, Swedish Rye, 

 and Improved Ligowa Oats. Attempts were made, extending over several 

 years, to change the parasiric propensities of P. grayninis tritict-compaeti , both 

 by the use of alleged bridging hosts, and by growing the rust for a period 

 of time on an uncongenial host. The authors" summary is as follows: 



(1) P. gramhiis tritiei-compacti was confined to barley and resistant wheat 

 for a number of successive generations, but it did not acquire increased 

 virulence for these hosts. 



(2) The parasitism of P. graminis tritici-eonipacti was not changed by 

 bridging hosts or by association with a given host. 



(3) Susceptible plants of the Fj generation of the cross Haynes 

 Bluestem X Knbanka did not enable the rust to infect seedlings of the 

 resistant parent normally, or to infect the susceptible parent more virulently. 



(4) The culture of stemmst on susceptible plants of the F, generation 

 of the cross White Spring emmer X Marquis had no appreciable effect on 

 the parasite. 



1 5) Negative results were obtained in attempting to alter the infection 

 capabilities of the rust by growing it for a generation on susceptible Fj 

 plants of the cross Marquis X Kubanka. 



(6) Fj hybrids of the cross Haynes Bluestem X Kubanka were appa- 

 rently homozygous for morphological characters, but heterozygous for the 

 character of rust resistance. Susceptible hybrid plants did not act as bridges 

 for the rust. 



(7) The resistance of wheat varieties may vary in different regions 

 because of the presence of different strains of rust. 



(8) There seems to be little basis for the belief that hybrids between 

 resistant and susceptible varieties will exert a harmful final effect by in- 

 creasing the virulence and host range of stemmst. 



M. S. Pease. Cambridge. 



Hertwig. Paula. Haploide und iliploide Parthenogenese. Biol. Zentral- 

 blatt. 40. S. 14.5—174. 



Die Abhandlung bringt unter besonderer Berücksichtigung der Chro- 

 matin-Yerhältnisse eine übersichtliche gedrängte Darstellung der bisher be- 

 kannten Tatsachen über Parthenogenese. 



A. Zunächst werden die Fälle künstlicher Entwicklungsanregung bei 

 Tieren betrachtet — Anregung durch chemische Mittel (Loeb, Delage u. a.), 

 durch physikalische Mittel (Anstich u. a.), durch biologische Mittel (Be- 

 fruchtung mit radiumbestrahltem Samen). 



Die Chromosomenzahl. haploid oder diploid, steht in Beziehung dazu, 

 ob der künstliche Eingriff Eier mit schon reduzienem oder noch nicht re- 

 duziertem Chromosomenbestand trifft. Damach entstehen haploide oder di- 

 ploide Keime und unterscheidet P. Hertwig haploide und diploide Partheno- 

 genese. 



Die Verf. erörtert eingeHend die Frage, ob derartig parthenogenetisch 

 ent.standene haploide Organismen zu geschlechtsreifen Tieren heranwachsen 

 können. Versuche, solche haploide Individuen sonst diploider Formen hoch 

 zu züchten, haben bisher höchst geringen Erfoig gehabt (^Seeigel, Rhabditis 



