ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
323 
derived from the embryo cell, which first becomes divided transversely 
into a number of segments. The terminal segment of the row thus 
formed gives rise to the cotyledon, the second to the stem, and tho third 
and fourth to the root. Iu Zannichellia the terminal segment divides 
vertically, one half becoming converted into the cotyledon, and the 
other half into the stem ; the second, third, and fourth segments give 
rise to the root, and the fifth to the root-cap. In Naicis jiexilis the 
embryo has no trace of a root-cap. In both genera the endosperm is 
rudimentary. In the later stages of the embryo-sac of N. jiexilis there 
is always present near the antipodal cells a large nucleus, which in- 
creases to an enormous size, but does not undergo division. The stamen 
of N. jiexilis is surrounded by two envelopes, the inner of which is 
regarded by the author as the homologue of the ovular integument, and 
the outer one as corresponding to the carpel of the female flower. 
Embryology of Potamogeton.* — Mr. K. M. Wiegand has studied 
the origin and development of the embryo-sac, fertilisation, and deve- 
lopment of the embryo, in Potamogeton jparvijlorus. The embryo-sac 
arises, as is usual in Monocotyledons, from a hypodermal cell, after the 
cutting off of a tapetal cell. The egg-apparatus and antipodals are 
somewhat abnormal. The polar nucleus and the first and second 
synergids appear to have been cut off successively from the mother- 
nucleus of the oosphere. The synergids disappear almost immediately. 
The definitive nucleus cuts off a very large basal nucleus, as in Sagit- 
taria , before endosperm formation proceeds in the upper part of the 
embryo-sac. 
Embryo-sac of Hybrid Narcissi.f — According to Dr. A. Preda, in 
all the forms of hybrid Narcissi examined the nuclei of the synergids 
and that of the oosphere are erythrophilous ; and the same is the case 
with the secondary nucleus. On the other hand the nuclei of the anti- 
podals are strongly cyanophilous. It is, therefore, incorrect to speak of 
the nuclei of the embryo-sac as being always erythrophilous. 
Theories of Heredity .J — Mr. W. T. Swingle dissents from Weis- 
mann’s theory of reduction of chromosomes. Arguing from the extreme 
polymorphism often displayed in the first generation of hybrids between 
races of cultivated plants, or between closely related species, he considers 
it necessary to assume, in some cases at least, a predetermination of the 
characters of the hybrid at the time of fusion of the male and female 
nuclei. The male and female chromosomes probably persist side by 
side unchanged in number, during the whole of the ontogeny of the 
hybrid, reduction not occurring until the close of the first generation. 
(2) Nutrition and Growth (including- Germination, and Movements 
of Fluids). 
Action of Organic Acids on Growth.§ — Experiments made by Sig. 
G. Lopriore on the action of organic acids — citric, malic, tartaric, tannic 
— on the growth of pollen-tubes showed a uniformly favourable result, 
but a specific variation in the influence of different acids of the same 
* Bot. Gazette, xxv. (1898) pp. 116-7. 
t Arch. Sci. Phys. ct Nat., iv. (1897) p. 590. 
X Bot. Gazette, xxv. (1898) pp. 111-13. 
§ Bot. Zt", lv. (1897) 2 tc Abth., pp. 362-3. 
