The Periodic Reduction of the number of 
the Chromosomes in the Life-History of 
Living Organisms 1 . 
BY 
EDUARD STRASBURGER. 
T HE simplest organisms with which we are acquainted 
reproduce themselves in only an asexual manner. It 
would appear that it is only in the lowest organisms that the 
absence of sexual differentiation is possible, and that this 
differentiation necessarily accompanies a certain definite 
degree of organization : it is, in fact, as if this differentiation 
must manifest itself at a certain stage of phylogenetic evolution 
in virtue of certain properties possessed by organized matter 
as such. It is true that many highly organized plants are 
asexual, but comparative investigation proves that this is due 
to a gradual loss of sexual differentiation, as in the great 
group of the Fungi, and doubtless also in the apogamous 
Ferns. 
It appears that the sexual act has always given a powerful 
impulse to phylogenetic evolution ; and that, on the other 
hand, all advance in development was in abeyance so long as 
sexual differentiation had not been obtained. From the 
phylogenetic standpoint, we must assume that all sexually 
differentiated organisms are descended from asexual organ- 
isms. The process of this descent is clearly illustrated in 
1 Translation of a paper communicated to Section D of the British Association, 
Oxford meeting, August, 1894. 
[Annals of Botany, Vol. VIII. No. XXXI. September, 1894.] 
