104 GENETICS [Bot. Absts., Vol. IV, 



643. Kuwada, Y. Die Chromosomenzahl von Zea Mays L. Ein Beitrag zur Hypothese der 

 Individuality der Chromosomen und zur Frage uber die Herkunft von Zea Mays L. [The 

 chromosome-number of Zea mays L. A contribution to the hypothesis of the individuality of 

 chromosomes and to the problem of the origin of Zea mays L.] Jour. Coll. Sci. Imperial Univ. 

 Tokyo 39: 1-148. 2 -pi., 4 fig. Aug., 1919. — Haploid chromosome-number, in starchy maize 

 as "Black Starch," "Amber Rice Pop Corn," "Black Mexican," is 10, and fluctuates rarely 

 into 7, 8, 9, while that in sugar-maize, or "Sugar Corn," is 12, and fluctuates very often into 

 9, 10, 11, 13, or 14; the diploid number which was studied in the root-tips, is generally 20. In 

 some races of sugar-maize author finds that the chromosome-number in the root-tips is variable 

 in different individuals of one and the same race, for it is sometimes 20, 21, 22, sometimes 23, 

 24; in such cases the haploid number is correspondingly variable and is 10,11 or 12. On the 

 basis of comparative studies on the number and length of pairs and the length of chromo- 

 somes in the root-tip author comes to the conclusion that the number of chromosomes in a 

 nucleus may increase by the transverse division of some of them, thus, for example, 24 

 chromosomes are equal to 20 entire ones + 4 fractional, which were produced by transverse 

 division of each of the remaining chromosomes into two. Further, author has found that 

 Euchlaena has 10 (haploid) and 20 (diploid) chromosomes which are long, and also that 

 Andropogon has the same number of chromosomes which are distinguished by their short- 

 ness; in the nuclei of maize there are found two types of chromosomes, long and short, so that 

 chromosomes which are apparently homologous may be of different lengths and even one 

 and the same pair is sometimes composed of two chromosomes of different lengths. From all 

 these facts author thinks as does Collins that Zea Mays was originally derived from the 

 hybridization between Euchlaena and some unknown species of the tribe Andropogoneae, 

 long chromosomes belonging to the former and short ones to the latter, and that the nuclei 

 of its various individuals possess both kinds of chromosomes in various combinations accord- 

 ing to the law of chance. As both Euchlaena and Andropogon have 10 chromosomes as hap- 

 loid number, their original number in Zea Mays will be 10, 12, etc., being derived from 10. 

 The chromosomes derived from Euchlaena (long) have the tendency to undergo the transverse 

 division, so that in synapsis each such chromosome either presents itself as two fractional 

 ones or remains single and retains that tendency, while those derived from Andropogoneae 

 (short) have no such tendency at all and remain always single. When in synapsis the two 

 fractional chromosomes of Euchlaena origin derived from one chromosome by transverse divi- 

 sion on one side and a single one of the same origin retaining the tendency of dividing on 

 the other happen to form together a geminus, the single one is generally compelled to divide 

 transversely into two by the influence of the fractional companions, so that in such case the two 

 fractional chromosomes may be said to be "dominant" to the single one, though sometimes 

 exceptions may occur; the number of chromosomes is therefore variable in different cases. 

 When, on the contrary, the two fractional chromosomes come to form a geminus together with 

 a single one originating from Andropogoneae having no tendency to divide, the former are 

 always compelled to fuse to each other, end to end, owing to the influence of the latter, so 

 that in all such cases the former may be said to be "recessive" to the latter; the chromosome- 

 number is always constant in such cases. The variability of the chromosome-number, haploid 

 as well as diploid, in various individuals, even in one and the same race, may be easily com- 

 prehensible, because there will be according to individuals different modes of combinations 

 of different gemini as the consequence of fertilization, which are considered in detail by author. 

 Author also discusses various cytological and genetical subjects. — S. Ikeno. 



'. Kuster, Erxst. Uber weissrandige Blatter und andere Formen der Bimtblattrig- 

 keit. [On white-margined leaves and other forms of variegation.] Biol. Zentralbl. 39 : 212-251. 

 27 fig. May, 1919. — Variegated leaves and shoots having green and colorless areas more or 

 less sharply delimited are divided into three groups: marginal, sectorial, and mottled or pul- 

 verulent variegation. Consideration is given primarily to marginal variegation which is di- 

 vided into four types: (1) P< largonium zonale type, with green leaves having a white border of 

 varying width around the entire leaf. (2) Saxifraga sarmentosa type, green leaves with a 

 white margin but on the margin is a sprinkling of small green areas. (3) Spiraea bumalda type, 



