548 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
in Ipomsea paniculata. They closely resemble in structure the glands 
of the pitcher of various species of Nepenthes. On each side of the 
petiole is a depression which is covered by a thin colourless saccharine 
fluid secreted by a gland hidden within the tissue of the leaf. In the 
centre of the depression rises a small papilla, at the apex of which is a 
wide mouth, from which the secretion of the gland is poured over the 
surrounding concave surface. 
j8. Physiology. 
(1) Reproduction and Embryology. 
Chalazogamy of the Birch.* — Dr. S. Nawaschin gives a detailed 
account of the structure of the sexual organs in Betula , and of the mode 
of impregnation of the ovule. He regards chalazogamy as one of the 
intermediate stages between the intercellular growth of the pollen-tube 
in the gymnospermous ovary, and its free growth through the cavity of 
the ovary in Angiosperms. The first adaptation to the penetration of 
the pollen-tube through the chalaza lies in the formation of lateral 
ovules. In plants with a single terminal ovule chalazogamy is 
impossible. 
The author . traces the development of the typical angiospermous 
ovary through the following stages : — (1) An open ovary as in Conifer®, 
with central ovule consisting of nothing but nucellus ; (2) closing of 
the mouth of the ovary (unknown) ; (3) the ovule clothes itself with an 
integument, as in Juglans and Myrica , porogamy; (4) central placenta 
with two naked ovules, Loranthus ; (5) Alnus ; (6) Betula; (7) Ulmus , 
an intermediate condition between porogamy and chalazogamy ; 
(8) Typical Angiosperms. In the development of Dicotyledons two 
lines of descent have manifested themselves : — one, the Acrosperm.®, 
begins with a simple porogamous mode of impregnation ; while the 
other series, the Pleurosperm^:, have begun with chalazogamy, becom- 
ing afterwards porogamous. The apetalous Dicotyledons are probably 
descended from the Conifer® ; the Casuarine® from the Gnetace® ; the 
Monocotyledons from the Cycade®. 
Embryo-sac of Aster.f — Mr. C. J. Chamberlain has carefully ex- 
amined the structure of the embryo-sac of Aster Novse-Anglise. The 
mature sac is very elongated, and is surrounded by a strongly differen- 
tiated layer of tapetal cells. The embryonic vesicles fill up about one- 
sixth of the sac, the oosphere, which is pear-shaped or perfectly globular, 
occupying from one-half to four-fifths of its diameter. It contains a large 
vacuole, below which is the nucleus. The two synergids generally fill the 
entire diameter of the sac ; their nuclei vary in position. The endosperm- 
nucleus lies just below the oosphere ; it is very large, and has a large 
dense nucleole. The antipodals are invested with membranes, and vary 
greatly in number, from three to as many as thirteen, formed from the 
first cell by cell-division; they frequently contain a large number of 
nuclei. In the lowest of the antipodal cells the author has frequently 
found a structure closely resembling an oosphere. He regards this 
* Mem. Acad. Sci. St. Petersbourg, xlii. (1894). See Bot. Centralbl., lxii. (1895) 
p. 324. Cf. this Journal, 1894, p. 707, 
f Bot. Gazette, xx. (1895) pp. 205-12 (2 pis.). Cf. this Journal, 1893, p. 352. 
