ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
65 
fusion of tho two protoplasms, likewise of different origin, reprosentod 
essentially by the tinoleucitcs of tho male and female cell. 
After its entry into the pollon-tube, the reproductive cell of the 
pollen-grain is fusiform, and is provided with its own specialized proto- 
plasm, the tinoleucites being generally found at ono of its extremities. 
After this cell has divided into two, the anterior of the two, which alone 
takes part in tho process of impregnation, has its two tinoleucites in 
front of the nucleus. The oosphere, on the other hand, has its two 
tinoleucites above its nucleus. Consequently, when the male cell 
penetrates the female cell, tho tinoleucites of each cell first come into 
contact with one another, and fuse together in pairs. The two now 
tinoleucitcs thus formed then separate from one another in order to allow 
the two nuclei to unite in their turn ; they are the origin of the poles of 
the first spindle in the oosphero after impregnation. Fecundation is 
completed by tho gradual fusion of tho two nuclei and tho division of 
tho mass formed by the chromatic segments of the two sexual nuclei. 
The process corresponds closely to that observed by Fol * in tho case 
of animal impregnation. 
Function of Extrafloral Nectaries-t — Herr W. Burck describes a 
number of instances in tropical plants in which the corolla is invariably 
perforated by insects in order to obtain tho nectar, sometimes by the 
regular visitant of tho species, sometimes by altogether foreign insects. 
In order to counteract tho prejudicial effects of this absence of cross- 
pollination, the species so affected tend to vary in two directions, — 
towards the formation of extrafloral nectaries, which attract ants to 
destroy the injurious visitors, and towards contrivances for self-pollina- 
tion. Several tropical species are described in which tho oxtrafloral 
nectaries are situated, for this purpose, in close proximity to the flowor. 
Among those in which arrangements adapted for self-pollination have 
been developed are several species of Pharbitis and Ipomsea belonging to 
tho Convolvulacca;. Extrafloral nectaries are further described in tho 
following plants : — Memecylon rarnijiorum, species of Nepenthes (on tho 
outer side of the pitcher, attracting a considerable number of ants), 
Trichosanthos tricuspidata, and several species of Smilax. 
Polyembryony in Clusiacese.j: — In a monograph of tho morphology 
and anatomy of this order of Dicotyledons, M. J. Ycsquo records several 
instances of polyembryony in different species of Clusia. In all cases 
one of the embryos is much larger and more perfectly formed than tho 
rest ; in the other embryos — in one instance there were as many as six — 
the cotyledons are either entirely wanting or are very small. 
Self-fertilized Flowers.§ — Mr. T. Meehan adduces reasons for 
believing that a large number of Composite are self-pollinated, and that 
the explanation offered by Darwin and others of the conspicuous stcrilo 
ray-florets — viz. to act as signal-flags for the attraction of fertilizing 
insects — is inadequate. The author has observed pollen-tubes entering 
in the clefts of the bi-lobcd stigmas before they open ; and tho pollen- 
* Cf. this Journal, 1891, p. 447. 
t Ann. Jard. Bot. Buitenzorg, x. (1S91) pp. 75-144 (5 pis.). 
j Journ. de Bot. (Morot), v. (1891) pp. 328-30. 
§ Proc. Acad. Nat. Sci. Philadelphia, 1891, pp. 271-2, 276-83 (1 fig.). 
1892. f 
