276 AN INTRODUCTION TO MODERN GENETICS 



In lower organisms, Wettstein^ has described some very clear in- 

 stances of cytoplasmic inheritance in mosses. Crosses within the species 

 Funaria hygrometrica show ordinary Mendelian behaviour of the type 

 to be expected in organisms with an important haplophase; that is to 

 say, the gametes unite to give hybrid diploid sporophytes, whose 

 appearance is governed by the dominance relations of the genes in- 

 volved, and these sporophytes give haploid gametophytes which show 



Fig. 124. Cytoplasmic Inheritance of Male Sterility in Flax.— The male sterile 

 plants have much reduced petals and aborted anthers. They arise in crosses between 

 normal tall and low-growing "procumbent" plants, but only when a factor or 

 factors from the tall nucleus are present homozygous in procumbent cytoplasm. 

 Typical crosses are as follows: [T] = tall cytoplasm, Vf\ = procumbent cytoplasm, 



t factor or factors in tall nucleus concerned with male sterility, p procumbent 

 factors. (After Pellew.) 



1. Tall nn ti X Procumbent [T] pp 



F1 all male fertile, 



F2, etc., all male fertile. 



2. [p] pp X |T| tt 



F1 [7]pt 



F2 [p] P^ • 2 [p] pt : 1 |T] tt (male sterile) 



3. [p] tt X [T| tp (from 1) 



F1 1 [T]tt (sterile) : 1 [T| tp 



I selfed 

 1 p] pp : 2 [T] tp : 1 [T] tt (sterile) 



segregation. When crosses are made between two species of Funaria, 

 F. hygrometrica and F. mediterranean the same purely genetic inheri- 

 tance is found for some characters (e.g. shape of paraphyses), but in 

 respect of other characters the hybrids differ according to which species 

 was used as female parent and supplied the cytoplasm. Thus if we 

 symbolize the haploid gene complement of the two species by Hy and 

 Me, and the two cytoplasms as [h7] and [m7| , we find that the shape of 

 the capsules differs in the reciprocal hybrids [h7| HyMe and [Me] HyMe. 

 From the diploid sporophytes, diploid gametophytes can be obtained 

 by regeneration (cf. p. 213) and these show more numerous distin- 

 guishable characters, many of which show the same dependence on 

 ^ Wettstein 1926, 1927, 1928a. 



