ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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adiantifolia ( Gingko biloba). The mature pollen-grain consists of three 
cells of unequal size. The largest is the vegetative cell ; a small inter- 
mediate cell is the antheridial cell ; the smallest exterior cell takes no 
active part in the process. From the largest cell is produced the pollen- 
tube, which branches, and spreads over the inner surface of the nucellus ; 
the apex of one of these branches comes into contact with the neck-cells 
of the archegone. The nucleus of the intermediate cell divides, and the 
cell divides into a body-cell and a stalk-cell. The body-cell again 
divides, and two attraction-spheres appear at its poles. The daughter- 
cell is transformed into antherozoids, two in each pollen-tube. The cen- 
trosome elongates into a slender filament. The body of the antherozoid 
has, at its head, three spiral coils, on which the cilia are formed out of 
the centrosome. The antherozoids escape from the mother-cell, and 
swim freely in the liquid contained in the pollen-tube. 
Fertilisation in Cycas.* — Prof. S. Ikeno gives further details of the 
development of the sexual organs and the process of impregnation in 
Cycas revoluta. The former agree essentially with those in other Gymno- 
sperms. 
In the formation of the archegone, three periods may be distinguished, 
— the “ primordium ” period, the growth period, and the maturity period. 
The pollen-grain consists of two small prothallium-cells and a large 
embryonal cell. Shortly after pollination, the pollen-grain produces a 
tube which penetrates the nucellar tissue. The nucleus of the inner pro- 
thallium-cell divides into a body-cell nucleus and a stalk-cell nucleus. 
The latter is pushed aside ; while in the former appear two centrosomes, 
which rapidly attain a very large size. The embryonal cell nucleus 
follows the body-cell nucleus, so that, shortly before the formation of 
the antherozoids, the outer prothallium-cell nucleus, the body-cell 
nucleus, the nucleus of the embryonal cell, and that of the pedicel-cell, 
all meet at the closed end of the pollen-tube. Shortly before impregna- 
tion, the nucleus of the body-cell or spermatogenous cell divides into 
two nuclei, and the cell itself into two spermatids. The nucleus of each 
spermatid developes into an antherozoid with a nucleus and a tail 
composed of cytoplasm. Shortly before, or shortly after, the entrance 
of the antherozoid, a crater-like cavity is formed in the nucleus of the 
oosphere, into which the antherozoid enters in order to fuse with the 
oosphere-nucleus, penetrating gradually deeper into the latter. 
Fertilisation of Ulmus. f — M. S. Nawaschin has studied the progress 
of the pollen-tube in two species of elm, Ulmus joedunculata and montana , 
and regards it as exhibiting a phenomenon intermediate between chala- 
zogamy and porogamy. The ovary is unilocular — not bilocular, as some 
have considered — and contains a single pendent ovule. The course of the 
pollen-tube in Ulmus is not uniform. In the great majority of cases it 
penetrates the tissue of the funicle close to its edge, and then pierces the 
inner integument to reach the apex of the nucellus. In other cases the 
pollen-tube branches profusely, and shows a distinct tendency to grow 
outside the tissue of the nucellus. In other cases, again, the pollen- 
* Jahrb. f. wis8. Bot., xxxii. (1898) pp. 557-602 (3 pis., 2 figs.). Joum. Coll. 
Sci. Tokyo, xii. (1898) pp. 151-214 (8 pis.). Cf. this Journal, 1897, p. 140. 
t Bull. Acad. Imp. Sci. St. Petersbourg, viii. (1898) pp. 345-57 (1 pi.). See 
Bot. Centralbl., lxxvii. (1899) p. 2G. 
