Noteworthy anatomical and physiological researches. 
The periodic reduction of chromosomes in living or- 
ganisms. 
Under this title Professor Eduard Strasburger communi- 
cated a very important paper to section D of the British As- 
sociation last August. A translation of the paper appears in 
the Annals of Botany for September, and so many of our 
previous views are affected by it that it deserves a somewhat 
full mention. 
Calling attention in the outset to the fact that sexual dif- 
ferentiation in plants was preceded by asexuality, the author 
shows that when this differentiation was attained it finally led 
to the production of a new generation set apart to spore pro- 
duction, and that in alternation of generations the sporophyte 
is the newer generation, having arisen from the gametophyte. 
In the production of this sporophyte it has been noted that 
the two gametes concerned have nuclei containing half the 
number of chromosomes characteristic of the nuclei of the re- 
sulting sporophyte, and this reduction has been regarded asa 
special preparation for the sexual act. Upon this hypothesis 
there have been constructed various theories with regard to 
the reduction and to the significance of the sexual act. Stras- 
burger and other observers find, however, that this reduction 
in the number of chromosomes in the generative nuclei of 
angiosperms is determined in the mother-cells of the pollen 
and embryo-sac, and not during the maturation of the sex- 
ual cells. The physiological utility of this reduction is evi- 
dent in the prevention of the indefinite increase of chromo- 
somes with every succeeding generation and in securing the 
€qual representation of each parent. The morphological 
Cause, however, is phylogenetic, for it is simply a return to 
the original generation which had attained sexual differentia- 
tion, and which in consequence had developed as offspring 
Sporophytes containing nuclei with double the number of 
chromosomes. This reduction, therefore, is not the outcome 
of a Sradually evolved process of reduction, but is the sudden 
reappearance of the primitive number of chromosomes as it 
©xisted in the nuclei of the generation in which sexual differ- 
[23] 
