\ 



^^ 



356 INTRODUCTION TO CYTOLOGY 



Monoploid Sporophytes. — In a number of angiosperm genera, 

 individual plants have occasionally appeared with the gametic rather than 

 the zygotic number of somatic chromosomes. ^^ In several of these, 

 including Datura stramonium, Zea Mays, Crepis capillaris, (Enothera 

 Hookeri, and Triticum monococcum, it has been shown that the comple- 

 ment is truly monoploid (Fig. 203). The evidence at hand indicates that 

 such monoploid sporophytes, which are relatively rare, usually arise as the 

 result of the parthenogenetic development of the egg. Since only one 

 chromosome of each kind is present in the sporocyte, there is no normal 



synapsis, all of the chromosomes appearing as univa- 

 ^^^ ^^ lents at the end of the meiotic prophase. The dis- 

 7m^ tribution of these chromosomes is not the same in 



• all cases. In Datura they are distributed at random 



to the two poles in / and divide in //. Although 

 the plants are highly sterile as a result of this 

 irregularity, occasional spores with all 12 chromo- 

 somes are developed, so that selfing yields a few 

 diploid offspring. In CEnoihera Hookeri a random 

 distribution of the seven chromosomes occurs in 

 _ „„„ „ about one-quarter of the sporocytes; in the remainder 



Fig. 203. — Somatic ^ , r 



chromosome com pie- there is a Splitting and separation of some or even 

 ments from roots of ^^l of the chromosomes and a second splitting may 



monoploid and diploid .t7-/t^i-\ t -h i-i 



plants of Crepis capii- follow m // (Bleier). In the practically monoploid 

 laris {After Hoiiings- MattUola (7 + a fragment) some of the sporocytes 



head, 1930c.) . ,. ., . 



show irregular distribution oi the chromosomes, 

 while the majority show a splitting of all of them in the single 

 mitosis occurring. The dependence of fertility upon diploidy is well 

 illustrated by a monoploid and sterile Crepis plant which produced a 

 diploid and fertile branch. Even in this branch, however, synapsis was 

 somewhat deficient, indicating that diploidy and homozygosity do not 

 always insure fully normal meiotic regularity. 



Other Features of Autoheteroploids. — Tetraploid mutants are 

 frequently somewhat larger than the corresponding diploids; this is true 



1^ E.g., Datura (Blakeslee et al, 1922; Blakeslee and Cartledge, 1926, 1927; Belling 

 and Blakeslee, 1923, 1927); Crepis capillaris (Hollingshead, 1928a, 1930c); Matthiola 

 (Lesley and Frost, 1928); Nicntiana glutinosa (Goodspeed and Avery, 19296); Nico- 

 tiana tabacum (Clausen and Mann, 1924; Chipman and Goodspeed, 1927; Ruttle, 

 1928; see our p. 365); Solaniim (J0rgensen, 1928); Triticum (Gaines and Aase, 1926); 

 Lycopersicum (Lindstrom, 1929; Lindstrom and Koos, 1931); (Enothera (S. H. Emerson, 

 1929; Gates, 19296; Gates and Goodwin, 1930; Davis and Kulkarni, 1930; Bleier, 

 1933a; Catcheside, 1932); Zea (Stadler and Randolph, 1929; Randolph, 1932); Oryza 

 (Morinaga and Fukushima, 19316). 



In his paper on (Enothera (1933o; see also 19336) Bleier classifies known sporophytes 

 with the gametic chromosome number (these he calls "haplodiplonts") according to 

 whether this number is truly monoploid or not, and discusses the bearing of their 

 chromosome behavior on certain problems of meiosis. 



