448 BREAKDOWN OF GENETIC SYSTEMS 



parthenogenetic offspring is indicated in a trisomic diploid (Enothera 

 franciscana (2n = 15), itself derived from a haploid seedling (Stomps, 

 193 1). Such a predisposition is equally to be regarded as a condition 

 of diploid parthenogenesis, for failure of reduction in itself is no 

 stimulus to parthenogenesis, it merely permits repetition of the 

 lapse. 



In connection with non-recurrent parthenogenesis two other 

 errors of fertilisation, both occurring under normal conditions, may 

 be mentioned. It has been possible to show in Drosophila, from 

 genetical considerations, that a single, mosaic, zygote may develop 

 from two separately fertilised eggs sticking together (Stern and 

 Sekiguti, 1931) and from a binucleate egg, the two nuclei of which 

 were separately fertilised (Stern, 1927 ; cf. Goldschmidt and 

 Katsuki on Bomhyx, 1931 ; and Whiting on Habrobracon, 1935). 



(ii) Regeneration and Apospory. By injury or by vegetative 

 propagation it is possible to " regenerate " the gametophyte of a 

 liverwort (Marchals, cf. 191 1) or a moss (v. Wettstein, 1924) from 

 the diploid tissue of the sporophyte. The new gametophyte has 

 escaped meiosis and is therefore diploid. This is artificial and 

 necessarily non-recurrent apospory. From the diploid gametophytes 

 tetraploid sporophytes are obtained, and by repeating this process 

 V. Wettstein has succeeded in obtaining octoploid sporophytes. 

 This is possible only in monoecious forms like Amblystegium 

 (Marchals, 191 1). In dioecious species the 2 A + 2X and 2^ + 2y 

 gametophytes do not give functional gametes. The same effect 

 has been produced in the fern, Osmunda (Manton, 1932 ; cf. 

 Schwarzenbach, 1926 ; Lawton, 1932). 



A more complicated condition has been found by Andersson- 

 Kotto (1931, 1932 ; Andersson-Kotto and Gairdner, 1936) as a 

 result of mutation in the fern Scolopendrium vulgar e, but being 

 heritable the anomaly is recurrent. When the gametophytes from 

 this plant were intercrossed (a process analogous to self-fertilising a 

 flowering plant) one-quarter of the progeny developed the mutant 

 character, which is therefore a mendelian recessive. The character 

 consists in the development of gametophytic tissue on the fronds 

 of the sporophyte. There is no spore formation or meiotic process 

 of any kind at this stage. The gametophyte, therefore, has the 



