292 Ishikawa.—Studies on the Embryo Sac 
tion of safranin and light green, on which every detailed structure is shown 
up most brilliantly. Fig. 16 is delineated from a section stained with a com¬ 
bination of light green and iron-alum-haematoxylin; the plasma sheath ( p.s .) 
stained with the former is beautifully differentiated from the surrounding 
plasma mass (//.), which is stained dark with the latter. In Fig. 13 and 
Text-fig. IV two male cells are lying side by side, while in Fig. 14 one 
of them is situated a little way down towards the pole nucleus, and through 
the other male cell the egg nucleus (e.n.) is visible. In Fig. 16 only one of 
them is illustrated. At the moment of the fusion, the sperm nucleus (; m.n .) 
bears no plasma sheath (Fig. 15), the latter being probably cast off before¬ 
hand. At any rate in Oenothera the male products arrive at the female 
organ as sperm-cells, but not as sperm nuclei. The question whether the 
sperm nuclei are naked or not has been fully discussed by Strasburger (67), 
Kornicke (35), Nawaschin (47), and Welsford (75), who agreed as to the 
absence of the plasma sheath in Liliinn. On the other hand, Juel (34) has 
reported that he observed in Saxifraga granulata a thin plasma mass, 
attached on each of the sperm nuclei, which just slipped out of the synergids. 
Nemec (49) has described in Gagea lutea that the sperm nucleus is covered 
with a thin plasma mass lying in the synergid. A similar case has been 
also reported by Shattuck (61) for Ulmus americana,vj\io states that ‘the 
male cells lose their cytoplasm on entering the pollen-tube, and during their 
journey to the embryo sac are simply elongated nuclei. After entering the 
sac the nuclei become spherical and begin to gather a small amount of 
cytoplasm around them.’ Nawaschin in 1909 (46), and later in 1915, 
working with Finn (48), observed in Juglans nigra and J. regia that two 
sperm nuclei either in the pollen-tube or embryo sac are always found 
embedded within a common vesicular sheath, which they state to be 
the residue of the cytoplasm of the generative cell, though it is cast off before 
fertilization. Pace (51) is another investigator who gave a description of the 
occurrence of the granular plasma sheath around the sperm nucleus, when 
the latter is lying in the synergid, in Parnassia palustris . Recently 
Tchernoyarow (70) stated that in Myosurns minimus two male nuclei 
are enclosed in a common plasma sheath up to the moment of fertilization, 
when they cast off the cover in the embryo sac. These results indicate that 
possible existence of such a sperm-cell may be detected, if closely examined, 
in not a few families of the Angiosperms. 
Modilewski (42) has reported entry of the vegetative nucleus into the 
embryo sac, though no trace of such has been found by the writer in the sac, 
nor even in the end of the tube just before shedding, as already stated above. 
Only the degenerating synergid nucleus has often been observed as a 
chromatic globule in the attacked synergid, as shown in PI. VII, Figs, 13, 
15, s.n ., and in Text-fig. IV, s.n. Although it is in a degenerating condition, 
the vegetative nucleus is quite different from the chromatic nucleus of the 
