390 INTRODUCTION TO CYTOLOGY 



In Melandrium album {Lychnis olhaY^ an XF pair behaves essentially 

 as in Elodea (Fig. 223). This holds also for Ly chilis dioica, in which the 

 staminate plants have long been known to be heterozygous for sex 

 (Shull). In seeking an explanation for the preponderance of carpellate 

 plants in this genus, Correns found that the pollen tubes formed by 

 "female-producing" grains grow more rapidly than those of the "male- 

 producing" grains and thus reach a larger proportion of the ovules. 

 When relatively small amounts of pollen are used, thus lessening the 

 competition unfavorable to the male-producing pollen, the ratio of 

 staminate and pistillate plants among the offspring is 

 changed decidedly toward equality. ^^ 



A peculiar form of sex-chromosome behavior is 

 manifested by Rumex acetosa and certain related 

 species. ^^ In R. acetosa (Figs. 222, 224) the staminate 

 plant has 15 chromosomes in the somatic nuclei. In 



/g the microsporocytes there are six bivalents and a triple 

 f group composed of a large X with two smaller elements 



^ "s^^^^^i^ ^^^ ^^^ ^2-^ attached to its ends. In the first meiotic 

 ^^?o 'pQjT^ mitosis X disjoins from Fi and F2, and in the second 

 <:^7/ Dl ^ mitosis all of the chromosomes divide; hence two 



5;^ microspores of the quartet receive 7 chromosomes 



matic chromosome (6 + X) while the Other two receive 8 (6 + F1F2). 

 complements of car- rpj^^ somatic nuclei of the carpellate plant contain 



pellate (XX) and -t^-t^s rr^, 



staminate (YXY) 14 chromosomes (12 + XX). Thus it appears that 

 plants of Rumex fertilization by a male gamete with X results in a 



acetosa. Sex-chro- -^ i i i • i Tr t^ • 



mosomes in black, carpellate plant and that by a gamete with 1 1F2 in a 

 (After Ono, 19306.) gtaminate one. This may be called the XYn or YXY 

 type of sex-chromosome behavior. It is reported that in R. acetosella the 

 large chromosome and one small one disjoin from the other small one (Fig. 

 223, d). 



A similar triple chromosome group is found in Humulus japonicus.^^ 

 The distribution of the three members differs in the various sporocytes, 

 giving different chromosomal races (Tuschnjakova). The full sig- 



30 Blackburn (1923, 1924), Winge (19236), Heitz (19256). Other cases are Populus 

 and Valeriana (Meurman, 1925), Moras, Cannabis, and Salix (Sinoto, 1928), and 

 Silene (Blackburn, 1928, 1929). 



31 G. H. Shull (1910, 1911), Correns (19186, 19206, 1921, 19226). 



»2 Kihara and Ono (1923o6, 1925, 1926), Ono (1926, 1927a, 1928, 1930a6), Ono and 

 Shimotomai (1928), Meurman (1925), Kihara and Yamamoto (1931). The presence 

 of two kinds of pollen was demonstrated by Correns (19226). 



33 Kihara (1928, 1929a), Winge (19236, 1929a), Sinot6 (19296), Tuschnjakova 

 (1929, 1930). It seems probable that more complex configurations observed here 

 (Kihara, 1929f/) and in H. lupulus (Sinoto, 1929a6) are due to more extensive chromo- 

 some association (Winge, 19296), possibly through translocation. 



