SOME PROBLEMS OF REPRODUCTION, 55 
rods, into which the chromatin of the nucleus resolves itself 
in the early stages (prophases) of mitosis. 
It appears to be the rule that, apart from gametes and their 
antecedent cells, all the nuclei of a given species have the same 
number of chromatomeres ; each of these during mitosis splits 
into two, lengthwise, and one half goes toeach daughter-nucleus. 
In most flowering plants the normal number of chromato- 
meres in the vegetative cell is 16; at a certain stage, anterior 
to the gametogonium proper, the chromatin wreath (which 
had shown 16 rods at its formation) now segments in its pro- 
phases into a smaller number than were present in the meta- 
phases and anaphases of the previous mitosis, which number 
is perpetuated in the gametogonia and gametes. Thus in 
Helleborus and most Liliacezx the reduced number is 12, 
two thirds the original; in the Liliaceous genus Allium it is 
8. But in Convallaria (Lily-of-the-valley ), also belonging to 
the same order, there is no reduction, and in Muscari (Grape 
Hyacinth) it is raised to 24. In Orchids, also, no reduction 
has been observed. 
The cell in which this reduction first takes place does not 
appear fully determined in all cases ; but we know this much, 
that in the male (anther) it furnishes vegetative as well as 
reproductive offspring. Forit occurs, according to Guignard, in 
the pollen mother-cell, which forms four pollen grains, each 
to produce a vegetative and a gametogenic nucleus. All 
these perpetuate the reduced number of chromatomeres by 
normal mitosis. 
In the female (ovule) this reduction is first shown by the 
original nucleus of the embryo-sac. In some cases, at least 
(Lilium Martagon), Guignard, whose recent account is 
slightly different from Strasbirger’s and from his own previous 
statements, has shown! that the normal number of chromato- 
tution des Noyaux cellulaires chez les Végétaux,” ‘Comptes Rendus,’ May 11, 
1891. See also Boveri’s ‘ Zellen Studien : Verhalten der chromatischen Kern- 
substanz b. d. Bildung der Richtungskorper u. b. d. Befruchtung,” in ‘Jen. 
Zeit.,’ 1890. 
1 “Nouvelles Recherches sur le Noyau cellulaire,” in ‘Ann. des Sci. 
Nat. Bot.,’ ser. 6, xx, p. 334, and ‘Const. des Noyaux.’ 
