Pinus silvestris. 
29 
tubes of Taxus also branch. In the Angiosperms too it is not 
uncommon for two or more pollen-tubes to be formed from 
one pollen-grain and to be continued for some distance 1 . 
Reduction of the number of Chromosomes. 
It has recently been shown that, in several plants, at least, 
there is a reduction in the number of chromosomes in those 
cells which give rise to the sexual apparatus, i. e. the mother- 
cells of the pollen-grains have a smaller number of chromo- 
somes than are found in the other cells of the plant, and this 
reduced number is preserved with great constancy in future 
divisions of the nuclei inclosed in the pollen-grains. Likewise, 
it has been shown in a number of cases that a reduced number 
is also present in the primary nucleus of the embryo-sac, and 
that this number corresponds with the number of chromosomes 
in the pollen 2 . Guignard, however, has shown that, in the case 
of the primary nucleus of the embryo-sac, all the nuclei 
resulting from its divisions do not preserve the reduced 
number of chromosomes. Thus, during the division of the 
primary nucleus of the embryo-sac of Lilium Martagon , he 
counted 12 chromosomes, and similarly he saw 12 in the 
nuclei arising from its upper half ; but in the divisions of the 
lower half 16, 20 and 24 chromosomes were counted. In the 
divisions of the secondary nucleus of the embryo-sac to form 
the endosperm the number of the chromosomes is variable ; 
but it is remarkable that the first division shows more chromo- 
somes than the other cells of the plant. 
E. Overton 3 also found that a similar reduction in the 
number of the chromosomes took place in the reproductive 
cells of Ceratozamia mexicana, Tsnga canadensis , Larix decidua, 
and Ephedra helvetica. He found in fact that, while the cells 
of the nucellus contained 16 chromosomes, those of the young 
endosperm contained but 8. From this fact Overton concludes 
1 Strasburger, Bef. bei den Phanerog. pp. 41, 44. 
2 Strasburger, Kern- und Zelltheilung, Jena, 1888, p. 51 ff., and 241 ff., and 
Guignard, Nouvelles Etudes sur la Fee. 
3 ‘ On the Reduction of the Chromosomes in the Nuclei of Plants.’ Annals of 
Botany, March, 1893. 
