164 BOTANICAL GAZETTE [AUGUST 
chromosomes are grouped in pairs, and not in tetrads in tetraploid nuclei. 
In the triploid nuclei of the endosperm of angiosperms, there are both paired 
and unpaired chromosomes. In the mother cells of polyploid plants there are 
always only bivalent chromosomes (gemini), and never a complex of more 
than two chromosomes as elements of the reduction plate. In triploid-nuclei 
of the sporophyte of hybrids which result from a union of haploid and diploid 
gametes, there are both paired and single chromosomes, and in the mother 
cells of such plants both paired and single chromosomes appear. From a 
study of the various pairings it seems that they depend upon an attraction 
between homologous chromosomes, so that this homology, rather than any 
maternal or paternal origin, determines the formation of pairs, and it may be 
possible that a pair of two homologous chromosomes may be derived from 
the same sex product. The increase in the number of chromosomes has often 
led to parthenogenesis (eiapogamy), but there is also parthenogensis without 
any increase in the number of chromosomes. 
The large number of chromosomes does not always result from i ciettaal 
division, but may be due to a transverse division, and in this case there is no 
increase in the size of the nucleus and no loss of sex occurs. Zoological litera- 
ture shows many instances of analogous phenomena. 
This paper suggests a wide range of problems for cytological investigation, 
and obviously it has an important bearing upon the theory of the individuality 
of the chromosome.—Cuartes J. CHAMBERLAIN. 
Sixteen-nucleate embryo sacs.—The ovule of Euphorbia procera“ has sev- 
eral hypodermal archesporial cells, each of which divides into a tapetal cell and 
a megaspore mother cell. The two reduction divisions take place in the 
mother cells, but are not accompanied by wall formation, so that each mega- 
spore mother cell now contains four megaspore nuclei, or rather, four mega- 
spores not separated by walls. At this stage all the tetrads degenerate except 
one, and in this each megaspore nucleus undergoes two successive mitoses, 
g rise to a 16-nucleate sac. Several other species of Euphorbia were 
examined, and all had a single archesporial cell and a typical 8-nucleate sac. 
MopiLewskr’ had previously shown that in the 16-nucleate stage of £. 
procera the nuclei are arranged in four tetrad-like groups, from each of which 
one nucleus moved to the center of the sac to form the endosperm nucleus. 
The micropylar group formed the egg apparatus and the chalazal group the 
antipodals, while the two lateral groups resembled the egg apparatus. Double 
fertilization was observed, the second male nucleus fusing with the four nuclei 
at the center of the sac, so that the endosperm nucleus resulted from the fusion 
of five nuclei. The chromosome situation was not determined. 
% MopILEWSKI, J., Weitere eae zur op tag einiger Euphorbiaceae. 
Ber. Deutsch. Bot. Gesell. 28:4 I oO. 
§ —__—, Zur re abtidane yon papers procera. Ber. Deutsch, Bot 
Gesell. 297: 21-26. pl. 1. 1908 
