86 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
period of impregnation the cavity of the ovary is entirely filled up by 
the orthotropous ovule, the surface of the placenta and the wall of the 
ovary being in contact with one another, and even coalescing in places. 
On each side of the placenta is a remarkable wing-like growth. The 
course of the pollen-tubes is entirely intercellular ; after they have 
penetrated the stigma, they make their way into the tissue of the style, 
and finally reach that of the ovary, advancing close to the stylar canal 
without actually entering either it or the cavity of the ovary. They 
finally reach the wing-like outgrowths of the placenta, ascending, 
through the chalaza, into the nucellus, and penetrating to the embryo- 
sac. During their course the pollen-tubes put out a number of branches, 
so that the tissue of the nucellus has the appearance of being veined by 
a number of tubes which surround the embryo-sac on all sides. 
In this, as in other cases, the author regards chalazogamy as the 
result of the inability of the pollen-tube to grow in an open cavity ; it 
occurs only in those species which are on the border-line between Gymno- 
sperms and Augiosperms. He was able to detect the nuclei of the pollen- 
tube within the embryo-sac. At this period there is no differentiated 
egg-apparatus or ovum-cell. Iu addition to the antipodals there are only 
a few free nuclei which perform the function of a female apparatus. 
The male nuclei appear to wander through the protoplasm of the 
embryo-sac until they meet and coalesce with one of these, and this 
coalescence constitutes the act of impregnation. 
Development of the Embryo in Angiosperms.* — Herr F. Ilegel- 
maier states, as the result of a large number of observations on plants 
belonging to a great variety of different natural orders of Angiosperms 
(Monocotyledons and Dicotyledons), that the position of the cotyledons 
in the embryo of ripe seeds by no means always corresponds to their 
position when first formed, as changes of various kinds very frequently 
take place during the development of the seed. In a great number of 
examples (e. g. Crucifer se>, Polygala vulgaris), ovules which have precisely 
the same position in the same ovary, exhibit, at the time of differentiation, 
quite different positions of the two cotyledons, one being incumbent, the 
other aecumbent. The difference cannot, therefore, be the result of geo- 
tropism. The author has investigated the causes, which, in the different 
cases, have determined the changes that have taken place in the posi- 
tion of the cotyledons ; these depending largely on the pressure exercised 
on them by the other portions of the embryo or by the surrounding 
endosperm or perisperm. 
Embryo-sac of Jeffersonia.f — Mr. F. M. Andrews has followed out 
the development of the embryo-sac in Jeffersonia diphylla (Berberideae). 
The more important points are stated as follows : — The embryo-sac 
arises as a hypodermal cell at the apex of the nucellus. This cell 
divides first into two cells, each of these again dividing. The lowermost 
of these four cells alone undergoes further development, and becomes 
the embryo-sac. The upper daughter-cell is occasionally divided into 
two by a neaily vertical wall. The antipodal cells are unusually 
large. 
* Cot. Ztg., liii. (1895) l te Abtli., pp. 143-73. 
f Cot. Gazette, xx. (1895) pp. 423-5 (1 pi.). 
