and Fertilization in Oenothera . 
289 
Two sperm nuclei were often found in the lower end of the tube, which 
lay just upon the embryo sac, but the vegetative nucleus was not associated 
with them, though Modilewski ( 42 ) observed and delineated both. Much 
attention was focused upon this question, but no vegetative nucleus 
happened to be found there at all. It may have been suspended at one of 
the nodal swellings of the tube, because it is often the case that the tube 
nucleus is found staying in such a place. Or it may have become absorbed 
in the tube plasm before it reached the embryo sac. The male nucleus is 
ellipsoid or ovoid, containing few chromatic masses besides one to several 
small nucleoli, and is surrounded by a distinct plasma sheath which presents 
itself as elliptical or lenticular in form (PL VII, Figs. 4, 5, 7). In some cases 
both of the nuclei are found embedded in a common plasma sheath (PI. VI I, 
Fig. 6). It is interesting to notice that a greater quantity of plasm is found in 
front of than behind the male nucleus. This fact suggests that the nucleus 
is dragged by the plasm, causing the movement of the male cell towards 
the embryo sac. Blackman and Welsford ( 4 ) noticed, in Lilium , that one 
of the male nuclei which was destined to fuse with the egg nucleus was 
smaller than the other. This was not the case in Oenothera , and both the 
nuclei are nearly equal in size. Neither Modilewski ( 42 ) nor Geerts ( 21 ) 
has described or figured the plasma sheath in Oe. Lamarckiana and in 
Oe. biennis. In a paper on Myosurus minimus , recently published by 
Tchernoyarow ( 70 ), there are many good illustrations of male nuclei, 
embedded in a distinct plasma sheath in the pollen-tube as well as in the 
plasma mass, which flowed out of the synergids, and spread upon the 
oosphere. According to this observer, the male nuclei shed the plasma 
sheath before the fusion, as in the case of Oenothera . The cases illustrated 
in his figures agree very well with those observed by the writer in Oenothera , 
except that two male nuclei always lie in a common plasma sheath. 
Fertilization. 
On reaching the apical end of the sac, the pollen-tube proceeds to the 
upper part of the synergid, but never directly passes to the egg-cell, though 
the latter is situated so close to the tip of the former. It has been observed 
only once that the tube happened to come to the upper end of the egg-cell, 
but, without visiting the latter, turned the way to the apex of the filiform 
apparatus. On arriving at the synergid the pollen-tube pierces the filiform 
apparatus first of all, and generally makes its way through the border 
line of two adjoining apparatus (PI. VII, Figs. 8, 10). As stated above, 
Habermann’s conclusion is that the chemotropic reaction of the pollen-tube 
is induced by glucose and proteid, which are poured out through the canals 
of the filiform apparatus from the store of the vacuole in the synergid. 
It just explains the behaviour of the pollen-tube of Oenothera. In some 
cases the end of the tube expands just upon the filiform apparatus, and the 
U 
