292 Sir as burger. — The Periodic Reduction of 
Henry H. Dixon 1 found it necessary, in his investigation 
carried on in the Botanical Institute of the University of Bonn, 
in the spring of 1893, to confine his attention to ascertaining 
the reduction by half of the number of chromosomes in the 
endosperm-tissue of Pinus sylvestris. It can, however, hardly 
be doubted that the reduction takes place in the mother-cell 
of the embryo-sac as it does in the mother-cell of the pollen. 
However, without going beyond what is actually ascertained, 
namely, that the reduction in the number of the chromosomes 
takes place in the developing endosperm long before the 
development of the archegonia has begun, there is sufficient 
evidence to prove that the number of successive divisions 
which the nuclei with the reduced number of chromosomes 
have to undergo is altogether different and without relation 
in the parallel male and female generations. For instance, in 
Biota orientalis only five nuclear divisions intervene between 
the mother-cell of the pollen and the development of the 
spermatic nuclei : the pollen-mother-cell divides twice ; the 
pollen-grain divides once, forming the small generative and 
the larger vegetative cell ; the generative cell divides once, 
and the anterior of the two cells divides in the pollen-tube, 
forming the two sexually functional cells 2 . With this are to 
be contrasted the very numerous nuclear divisions which must 
take place in the embryo-sac of this plant before tissue - 
formation begins, and, in addition, the number of nuclear 
divisions which intervene between commencing tissue-formation 
and the completed development of the archegonium. Dixon 3 
counted, in Pinus sylvestris, only eight chromosomes in the 
nuclei of the young endosperm, as also in the ovum at the 
time of the formation of the canal-cell : on the other hand, 
I had counted twelve chromosomes in the pollen-grains of the 
same plant 4 . From renewed investigation made in the 
1 Fertilization of Pinus sylvestris , Annals of Botany, Vol. viii, No. XXIX, 
p. 21, 1894. 
2 Strasburger, Ueb. das Verhalten des Pollens, &c., bei den Gymnospermen, 
p. 19- 
3 Loc. cit, p. 29 ff. 4 Ueb. das Verhalten des Pollens, Sec., p. 34. 
