306 Ishikawa.—Studies on the Embryo Sac 
a rule perpendicular to each other, and the one which is parallel to the main 
axis of the sac shares in the formation of two nuclei, of which the upper 
one is destined to become the egg nucleus. In Dicraea elongata , on the other 
hand, this relation is just reversed. Of the two sister nuclei brought about 
by the upper spindle, which is parallel to the axis of the sac, the lower one 
becomes the egg nucleus. The sac of Plumbagella micrantha is most aberrant. 
Although no account of the share of each nucleus in the 4-nucleate stage is 
given by Dahlgren ( 14 ), four nuclei give rise to one egg nucleus, two polars 
which unite, one antipodal which becomes disintegrated in the mature sac, 
and no synergid. Another curious fact regarding the behaviour of the tetra- 
nucleate sac in certain plants, such as Cypripedium and Gastrodia , is that one 
of the synergid nuclei fuses with the polar, thereby causing a real triple 
fusion at the fertilization. It is interesting to notice that the plants which 
have been reported as having a tetranucleate sac are all herbaceous, except 
Codiaeunt . Moreover those plants shown in the following list, which are 
recognized as having a 16-nucleate sac, due to four successive divisions 
of the megaspore nucleus, are also herbaceous. However, there is one 
exceptional case, which is found in Garcinia Treubii and G. Kydia. In these 
woody plants Treub ( 71 ) found a pentanucleate embryo sac. In Garcinia , 
when the embryo sac has attained a tetranucleate stage, one of the upper nuclei 
undergoes one more division, resulting in the production of a 5-nucleate sac. 
This is just the case with Aglaonema, studied by Campbell (6). The sac of 
Garcinia is, however, bisporic, while that of Aglaonema is tetrasporic. 
Other examples of pentanucleate sac have been recorded as occurring 
in Lazvia zeylanica by Magnus, in Oenone Imthurnii and Mour era fluviatilis 
by Went ( 76 ). In these cases the sacs are bisporic, as in the case of other 
species in the Podostemaceae, and the nucleus of the primary embryo sac 
cell divides once, the upper one of the daughter nuclei undergoing two 
successive divisions, and the sac finally becomes pentanucleate. Besides, 
Jussieua suffruticosa , Godetia Whitneyi, Fuchsia ‘ Mar ink a \ and F. pro- 
cumbens , have been reported by Tackholm ( 69 ) as abnormally producing 
two pole nuclei due to an extra-nuclear division. 
As having a 16-nucleate embryo sac the following twenty-seven species 
of plants have so far been recorded : 
Piperaceae : 
Peperomia pellucida 
i Campbell 
( Johnson 
1899 
1900 
P. Sintensii 
Brown 
1908 
P. arifolia 
)} 
Ji 
P. Ottoniana 
If 
P. hispidula 
Johnson 
1907 
P. reflexa 
Fisher 
f f 
P. veriicillata 
P. scandens 
If 
ff 
P. metallica 
P. Praseri var. resedaeflora 
ff 
ff 
