ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
359 
Ou the entrance of the pollen-tube into the embryo-sac, the male and 
female nuclei appear to exert an attractive influence on one another, 
dependent j)i't>bably on chemical causes, similar to that which seems to 
guide the antherozoids of Cryptogams towards the archegone. 
Embryo-sac of Compositae.* — Herr F. Hegelmaier describes the 
peculiarities in the structure and development of the embryo-sac in some 
species of Compositee, especially some belonging to the tribe Heliantheae. 
In Heliantlms annuus, at the time of the opening of the corolla and 
separation of the arras of the style, the innermost layer of cells of the 
thick integument has the form of a compact sheath ; the elongated 
cavity becomes filled up by the embryo-sac, with the exception of a small 
space lying between its own membrane and the inclosing sheath, and 
caused by the disappearance of the innermost layer of cells of the 
nucellus. The embryo-sac is itself divided by transverse septa into a 
row of three cells, the central and posterior of which must be regarded 
as antipod als, the anterior includes the large vegetative nucleus and 
the egg-apparatus. The two sterile synergidas are prolonged at their 
apex into slender conical points which project into the endostome. 
At the time of impregnation, the embryo-sac completely fills up the 
integument, the two posterior cells occupying from two-thirds to three- 
fourths of its entire space. 
Bidens leucantha and Zinnia tenuijlora present the same peculiarities 
as Heliantlms annuus in almost every respect; and others of the 
Heliantheae have the same structure in its general features. In Tussilago 
Far far a the base of the embryo-sac is occupied for about one-third of its 
length by a group of cells resulting from cell-division ; while in other 
genera belonging to the Cichoriaceae the group of antipodals has developed 
into a parenchymatous tissue. In the dandelion they are four or five in 
number, and form a single row in the narrowed conical posterior end of 
the embryo-sac. These characters are, therefore, of but little importance 
for purposes of classification. 
The innermost layer of cells of the integument above described, or 
endoderm, is especially developed in many, though not in all, ovules 
with a single thick integument, in which the nucellar tissue disappears 
entirely before impregnation, as in the Compositte, Valerianaceae, Dipsa- 
caceae, Campanulacem, Umbelliferae, and Araliacese; less often in ovules 
with a double integument, as in Linum. Its cells are elongated in the 
radial direction, cubical, or even tabular. The layers of cells of the 
integument next to the endoderm often begin to be converted into 
mucilage even before imj)regnation. 
Flowering of Amorphophallus.t— Dr. O. Beccari describes the 
flowering and formation of the fruit in Amorpho;pliallus Titanum, the 
flower of which is probably the largest in existence. The production of 
the colour and odour of decomposing raw flesh, which attracts insects 
for the purpose of impregnation, is ascribed to a much greater plasticity 
of the protoplasm in past ages than it at present manifests ; this being 
the basis on which natural selection and the struggle for existence 
worked. 
* Bot. Ztg., xlvii. (1889) pp. 805-12, 821-6, 8.S7-42 (1 pi.). 
t Boll. R. Soc. Toscana Orticultura, 1889 (3 tigs.). See Bot. Ceutralbl., xli 
(1890) p. 60. 
