290 Strasburger. — T he Periodic Reduction of 
are but three ; in Ornithogalum , Commelyna , and species of 
Agraphis , there are four ; in yet other cases the number is 
greater than five, as in Rosa livida 1 , in which case, it should 
be mentioned, the moment at which the reduction takes place 
has yet to be ascertained and thus also the identity of the 
cell established which functions as the mother-cell of the 
embryo-sac. In view of these facts, it is not surprising that 
in Scilla 2 and Ornithogalum the division of the spermatic 
nucleus in the pollen-tube may be repeated, so that often four 
spermatic nuclei are formed instead of two. The attempts 
which have been made to establish homologies between the 
individual successive divisions which precede the formation of 
the nucleus of the ovum, on the one hand, and those which 
precede the formation of the spermatic nucleus, on the other, 
are thus shown to be futile : and equally barren is the attempt 
to establish, on physiological grounds, the necessity for 
a certain definite number of nuclear divisions, based on the 
assumption that it is by these successive divisions that the 
male and female nuclei are brought to the same bulk. The 
whole process appears in an altogether new light when 
considered from the point of view that the reduced number 
of chromosomes in the mother-cells in question is the 
expression of the original ancestral number of chromosomes 
existing before the sexually-produced generation had been 
evolved. 
The reduction of the number of the chromosomes in the 
pollen-mother-cells of Angiosperms, which has been adduced 
as an example, is therefore not to be regarded as a preparation 
for the sexual act ; it really marks the beginning of the new 
generation which comes into existence with the primitive 
number of chromosomes. This primitive generation has, 
however, undergone great limitation before it attained the 
reduced ontogeny which it now exhibits in the Angiosperms. 
In the first place it developed sexual dimorphism, so that it 
1 Strasburger, Angiospermen und Gymnospermen, 1879, p. 14, Taf. IV. 
2 Strasburger, Neue Untersuchungen lib. den Befruchtungsvorgang bei den 
Phanerogamen, 1884, p. 17. 
