291 
Chr onto somes in Living Organisms . 
was represented by two parallel developmental series, a male 
and a female. The phylogenetic course along which this 
reduction, as also the development of the dimorphism, pro- 
ceeded, can be traced backwards. 
* Overton was the first to point out that, in the Gymnosperms 
also, the nuclei of the mother-cells of the pollen and of the em- 
bryo-sacs contain only half the number of chromosomes as com- 
pared with those of the plant developed from the ovum. He had 
already been rightly led by his researches on Lilium to raise 
the question 1 c whether the reduction may not take place, in the 
Vascular Cryptogams and the Mosses, in those cells which are 
the morphological equivalents of the mother-cells of the pollen 
and of the embryo-sacs of the Angiosperms ; in other words, 
whether the reduction does not take place in the mother-cells 
of the spores, that is, at the point of alternation of the 
generations.’ In the mother-cells of the pollen of Ceratozamia , 
Guignard 2 counted eight chromosomes, and found that this 
number persisted through the subsequent divisions. Overton 3 
found the same number of chromosomes in the developing 
endosperm in the embryo-sac. Guignard ascertained in 
Ceratozamia , and I in several Conifers 4 , that all the nuclear 
divisions in the mother-cells of the pollen and in the pollen- 
grains themselves are accompanied by longitudinal splitting 
of the chromosomes. At the same time I drew attention to 
the uniformity in the number of the chromosomes in the 
pollen-grains and ova of the Conifers; and I also suggested 
the probability that in Gymnosperms also the number of the 
chromosomes is determined in the mother-cell of the embryo- 
sac 5 . This last point still remains to be proved, since 
1 Ueb. d. Reduction der Chromosomen in den Kernen der Pflanzen, Viertel- 
jahrschr. d. naturforsch. Ges. in ZUrich, XXXVIII, 1893 ; also previously in Ber. 
d. Schw. Bot. Ges., Heft III, 1893; Jahresber. d. Ziiricher Bot. Ges., 1892-3, 
Sitzung von 21. Jan. 1892; and Annals of Botany, Vol. vii, No. XXV, 
March, 1893. 
2 Journal de Botanique, III, 1889, p. 232. 
3 Ueb. d. Reduction der Chromosomen, &c. 
4 Guignard, 1 . c. ; Strasburger, Ueb. das Verhalten des Pollens und die 
Befruchtungsvorgange bei den Gymnospermen, 1892, p. 34. 
5 Loc. cit., p. 35. 
