ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
303 
BOTANY. 
(Under the direction of A. B. Rendle, M.A., D.Sc., F.R.S., F.L.S.) 
GENERAL, 
Including- the Anatomy and Physiology of Seed Plants. 
Cytology, 
Including- Cell-Contents. 
Chromosomes and their Connexion with Heteroploid Varieties 
of Hyacinth us. —W. E. De Mol {Arch. Neerland. Sc. Ex. et Natur. 
Haarlem , 1921, 43B, 18-117, 13 pis.). An account of an investiga- 
tion as to the nature of the chromosomes of the numerous cultivated 
varieties of H. orientalis. The author sought to ascertain ( a ) if all the 
individuals which are looked upon as belonging to the same variety 
contain a corresponding number of chromosomes ; ( b ) if when a new 
variety has arisen at the expense of an old one by gemmary variation, 
it is possible to discover any divergence in the number or form of the 
chromosomes ; ( c ) if the cells of the Dutch varieties contain a variable 
number of chromosomes, and if these chromosomes show any variation 
in form or dimension. Both the present and previous investigations 
appear to show that there is such variation in the number of chromo- 
somes, and that the size of the nucleus and cells, and hence of the whole 
plant, is related to this variation. The cause of the variation seems to 
be physiological rather than cytological, although there is no evidence 
to prove that such artificial methods as wounding exert any appreciable 
influence in bringing about the necessary conditions. In the second 
series of experiments with gemmary variations it was not possible to 
show that there is any variation in the number, structure or form of 
the chromosomes ; but it seems probable that intimate alterations do 
occur both in the form and structure, although they have escaped 
observation owing to the minuteness of their detail. In 19 varieties 
of Dutch hyacinths the number of normal diploid chromosomes was 16, 
4 long, 4 medium and 4 short. In 14 heteroploid varieties the 
number varied from 19 to 30, but in this case also there were three 
different lengths; the forms and dimensions corresponded with those 
of the varieties having 16 chromosomes. The heteroploid varieties 
must have arisen as the result of fertilization and not by vegetative 
multiplication. A close examination of several varieties revealed no 
distinction between the chromosomes of the two parents. A new and 
exact method of measuring showed that in every case the sum of the 
lengths of a short and a medium-sized chromosome is equal to the 
length of the long chromosome. This fact taken in conjunction with 
other observations makes it probable that the shorter chromosomes 
arise by transverse division of the long ones. If this is correct the 
number is reduced to 12 in H. orientalis , and to 6 in H. romanus and 
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