450 



BREAKDOWN OF GENETIC SYSTEMS 



of change of chromosome number with the alternation of form in 

 succeeding generations is not due to a relationship of cause and 

 effect, but that the alternation of forms is a genetic property of the 

 race achieved by independent adaptation, immediately conditioned 

 by the stage in the cycle of development, and therefore independent 

 of the chromosome number. 



Table 67 

 Methods of Suppressing Meiosis with Diploid Parthenogenesis 



I . Little or no metaphase pairing Erigeron spp. 

 Restitution nucleus (as in 



Raphanus - Brassica Taraxacum spp. 



hybrids, cf. Fig. 127). Chondrilla 



Usually alternative to type 2. 



After a more or less meiotic 

 prophase the unpaired 

 chromosomes divide once 

 at metaphase (c/. Fig. 127). 



3. After a prolonged resting 

 stage a mitotic division 

 with mitotically contracted 

 or intermediate chromo- 

 somes replaces meiosis 

 (alternative to type 2). 



Double division of unpaired 

 chromosomes to give four 

 nuclei (as in Pygcsra 

 hybrids) . 

 Normal pairing and first 

 division with — 

 (i) Failure of second 

 anaphase. 



(ii) Reunion of two daughter- 

 nuclei at second telo- 

 phase. 



(iii) Fusion of nuclei in early 

 somatic division of 

 embryo. 



Ixeris 



Nephrodium . 



Balanophora 



Artemia (?) . 



Phylloxera 



Aphis palmcB 



Cynips and Rhodites 



Rhahditis sp. 



Daphnia 



Lecanium 



A rtem isia 



Archieracium 



Hieracium 



umbellatum. 

 A ntennaria . 



Eupatorium 



Poa serotina {cf. 

 Leontodon, Berg- 

 man, 1935 a). 



Bacillus rossii 



Cocconeis * . 



Thismia 



A rtemisia 



Cypris 

 Rhabditis 



monohystera. 

 Solenohia pineti 

 Artemia (i) or (ii) . 



Apotettix (ii) or (iii) 

 Solenohia 



triqi4,etrella. 

 Trialeurodes 



Holmgren, 191 9 



Carano, 1921. 

 Gustafsson, 1934. 

 Poddubnaja-Arnoldi, 



1933- 

 Okabe, 1932. 

 Steil, 1919. 

 Kuwada, 1928. 

 Fries, 1910. 

 Morgan, 1915. 

 de Baehr, 1919. 

 Hogben, 1920. 

 Belar, 1923. 

 Schrader, 1925. 

 Thomsen, 1927. 

 Chiarugi, 1926. 

 Rosenberg, 19 17. 

 Bergman, 1934. 



Stebbins, 1932 h 

 Bergman, 1935 a. 

 Holmgren, 1919. 

 Kiellander, 1935. 



V. Baehr, 1907. 

 Geitler, 1927. 

 Meyer, 1925. 

 Chiarugi, 1926. 



Woltereck, 1898. 

 Belar, 1923. 



Seller, 1923. 

 Brauer, 1894 ; Fries, 

 1910 ; Gross, 1935. 

 Robertson, 1931 c. 

 Seller, 1923. 



Thomsen, 1927. 



* Pachytene pairing seen. 



