293 
Chromosomes in Living Organisms. 
spring of this year, I come to the conclusion that both the 
pollen-mother-cells and the pollen-grains of Pinus sylvestris 
have only eight chromosomes. The counting of the chromo- 
somes in this material is attended with great difficulty, and is 
somewhat uncertain, for the limits of the individual chromo- 
somes are not clearly distinguishable, and moreover the 
chromatic segments in the chromosomes, when division is 
about to take place, are very distinct and often produce the 
impression of being independent chromosomes ; hence it is 
easy to conclude that the chromosomes are more numerous 
than is really the case. The nuclei in the nucellus and in the 
integuments of the same species of Pinus were found by 
Dixon to contain sixteen chromosomes, and my older 
preparations clearly show that the dividing nuclei of the 
developing embryo in the lower end (the morphological apex) 
of the ovum of Pinus sylvestris have more than eight, probably 
sixteen, chromosomes. They agree, as regards the number 
of the chromosomes, with the figures of Picea vulgaris which 
I published in 1880 h 
Overton 2 has already drawn attention to the fact that the 
processes which go on in the spore-mother-cells of the 
Vascular Cryptogams and the Mosses so closely resemble 
those by which the reduction in the number of the chromo- 
somes in the mother-cells of the pollen is effected, that their 
significance is probably the same in both. He found the 
actual determination of the number of the chromosomes to be 
attended with great difficulty in the Muscineae on account of 
the small size of the nuclei, and in the Pteridophyta on 
account of the large number of the chromosomes. As 
regards the Pteridophyta, although the number of the 
chromosomes is considerable in some of them, in others it 
is not greater than in the Phanerogams : for instance, in 
Osmunda regalis the chromosomes can be easily counted. 
I ascertained that there are twelve chromosomes in the spore- 
mother-cells of this plant. The differentiation of them in the 
1 Zellbildung und Zelltheilung, 3® Auflage, Taf. IV. 
2 Loc. cit. : p. 1 2 of the separate copy. 
