ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
709 
oldest cells of the embryo. As the cells of the suspensor, attached to 
the apex of the columel, elongatp, it forces the embryo towards the 
chalazal end of the embryo-sac. In its growth, the embryo does not 
gradually consume the whole of the endosperm, but only a special zone 
of it which is filled with food-materials. The final envelope of the seed 
is formed of a membranous pellicle proceeding both from the integument 
and from the nucellus, and of the “ shell ” which persists until the 
period of germination. 
Occasional Cleistogamy.* — Herr P. Graebner has observed the occa- 
sional occurrence of cleistogamous flowers, which nevertheless produced 
perfect seeds, in the following plants: — Gentiana Pneumonanthe, Gesnera 
bulbosa , Coleus aromaticus, Orobanche minor. The production of these 
flowers appeared to be the result of unfavourable climatal conditions. 
Cross- and Self-Pollination. — According to Sigg. G. Gibelli and 
L. Buscalioni,f the flowers of Trapa natans and T. Verbanensis are self- 
pollinated and cleistogamous. While still under water, the flowers 
remain closed, but open when exposed to the air, in consequence of the 
carpotropic curvature of the flower-stalk ; and by this time pollination 
has taken place. It is accompanied by an abundant excretion of nectar. 
Herr P. Knuth J has investigated the conditions of pollination in 
about 400 species of flowering plants growing in the islands of N. Fries- 
land. He states that among these, 4 species are hydrophilous, 145 
anemophilous, 12 self-pollinated, and 239 entomophilous ; in 167 of 
these self-pollination is possible. The proportion of anemophilous 
species is much larger than in Continental Germany. A detailed 
account is given of the visiting insects, and some remarks are appended 
respecting the structural peculiarities of the plants which inhabit these 
islands. 
Herr F. Heim § states that the flowers of Vincetoxicum officinale 
and Apocynum vepetum are visited both by diptera which assist in the 
pollination, and by injurious small flies. From the latter they are, 
however, to a certain extent protected by spiders. 
Mr. E. Walker || describes the mode in which the pollen is expelled 
from a terminal pore in the anther of Bichardia africana. The plant is 
proterogynous, and apparently dependent on insect-pollination. 
Experiments made by Miss M. Reed on cultivated varieties of Petunia 
appear to demonstrate the advantage of cross- over self-fertilization. 
Herr O. Ekstam ** gives some interesting facts regarding the pollina- 
tion of flowers in Nova Zembla. That country possesses three species of 
Pedicularis , which are self-pollinated, although there are several species 
of Bombus which are the pollinating agents of the genus in other arctic 
countries. In Nova Zembla they appear never to visit its flowers ; and 
* Yerhandl. Bot. Yer. Prov. Brandenburg, 1894, pp. 148-54. 
+ Rend. Accad. Lincei, ii. (1893) pp. 227-36. See Bot. Centralbl., 1894, Beih., 
p. 223. 
X ‘ Blumen u. Insecten d. nord-friesischen Inseln,’ Kiel, 1894, 207 pp. and 23 figs. 
See Bot. Centralbl. 1894, Beih., p. 225. 
$ Bull. mens. Soc. Linn. Paris, 1893, p. 1096. See Bot. Centralbl., fix. (1894) 
p. 245. || Bot. Gazette, xix. (1894) pp. 241-3. 
Tom. cit., pp. 336-7. 
** Ofv. K. Vetensk. Akad. Forh. Stockholm, li. (1894) pp. 79-84 (German). 
1894 3 C 
