Recent Work on the Reduction Division in Plants. 
9 
insensibly into the Central African Region, from which it has no 
doubt received the greater portion of its plants, while the presence 
of some Proteaceae such as Protea and Fauna saligua show that 
the somewhat more rigorous climatic conditions have preserved 
some forms of the older vegetation of South Africa, now for the 
most part surviving only in the south western Coast Region. The. 
separation of these Proteaceous trees from the bulk of the older 
flora in the SAV. can be explained by the barrier caused by the 
excessively arid conditions of the intervening portion of the 
Kalahari and the Karroo regions, which cannot support a tree-like 
vegetation. 
[Note.— I regret that I omitted to mention that the two 
photographs reproduced in Part I. were taken by my friend, 
Professor R. H. Yapp, who kindly allowed me to reproduce 
them. The Composite seen in the background of Fig. 1 of 
that Plate, turns out to be not Helichrysum , but Metalasia .] 
RECENT WORK ON THE “REDUCTION DIVISION” 
IN PLANTS. 
By Agnes Robertson. 
I.—The Facts of the Maturation Divisions. 
HE nuclear divisions which immediately precede spore forma- 
1 tion in plants, and egg and sperm formation in animals, have 
been of late the subject of much controversy. In the higher plants 
the “ spore mother-cell ” (embryo-sac mother-cell or pollen mother¬ 
cell as the case may be) divides, and the two daughter-cells have nuclei 
with half the somatic number of chromosomes. This first division 
is called the reduction division or lieterotypc (Flemming). Each of 
the two cells thus produced divides again, and so four spores are 
formed characterised by possessing half the somatic number of 
chromosomes. This second division is called the homotype 
(Flemming). The reduced number of chromosomes appears at each 
of the succeeding divisions by which the gametophyte or sexual 
generation is produced, up to the formation of the egg and sperm 
cells. This reduction is clearly necessary in order to prevent the 
number of chromosomes increasing in geometrical progression in 
each generation. The question of exactly how the reduction is 
brought about has been answered in very different senses by dif¬ 
ferent groups of observers. This answer is a matter of great 
importance from the point of view of theory, but we will defer for 
