Further Studies un the Apogamy and Hybridization of the Hit-racia. 27Q 



at once as Fj, or only later becomes so^). But here we only speak 

 about species hybrids which become constant in the first generation 

 and in which no segregation takes place, de Vries has called this 

 tj^pe the Hieracium type, as, referring to Mendel's experiments, he 

 took the Hieracium hybrids as the best known case of this form of 

 inheritance in hybrids. 



It appears, from what I have quoted here as well as from many 

 other remarks of de Vries, that he considers this non-segregating 

 type as rather widely spread, though only very few exact experiments 

 have been carried out to prove its existence. A concurrent cause 

 hereof is that species hybrids are so often quite sterile. A well known 

 example is the Verbasami hybrids, which very easily arise both in 

 nature and in Botanic Gardens, but which, as far as I know, are 

 always quite sterile. 



In contrast to DE VRIES, W. Bateson goes so far that he con- 

 siders the non-segregating hybrids as rare exceptions. In his recent 

 pubhcation "Mendel's' Principles of Heredity" (1909) he deals with 

 these exceptions in the first part of a particular chapter (XIV), which 

 he begins with the following words; "Of the various cases alleged to be 

 exceptional, or declared to be incompatible with MendeUan principles, 

 few have any authenticity. Several rest on errors of observation or 

 of interpretation and some have even been created by a mistranslation 

 or a misprint." The part of the chapter interesting to us here is 

 "Crosses breeding true without segregation" (pp. 246 — 251); it com- 

 prehends two sections, viz. A. Parthenogenetic cases, and B. Sexual 

 Types. 



The first section consists even of Hieraciinn, and Bateson here 

 briefly reports what has been known hitherto about the hybridization 



1) Of tliis case we have an example in Rubus. B. Lidforss ^1905, 1907) has by 

 experiments shown that new species in this genus can arise both by mutation and 

 by hybridization. As to tlie hybridization he has discovered the peculiarity that, while 

 F, most frequently is homogeneous and oftenest intermediate, there arises after self- 

 fertilization a very polymorphous Fg the heterogeneity of which, at any rate in part, 

 must be supposed to be called forth by a mutation released by the hybridization. 

 Also F2 is inconstant, but in a less degree, and it seems as if constancy increases 

 with the number of generations, so that constant new forms finally can be produced 

 in this way. 



.As to the well known polymorphy in Rubus, it must be remembered that each 

 individual has, practically seen, an indefinite lifetime and is able to form whole stocks 

 by propagating only vegetatively. Thus both Fj as well as the multifarious forms 

 of F2, etc. can respectively keep to the spot where they have risen, even if they 

 do not give constant offspring sexually. 



