ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 279 



divides into two, and each of these again into two derivative nuclei ; 

 thi-ee of these constitute the " egg-apparatus " ; the fourth, which 

 again moves to the centre of the embryo-sac, is the last product of 

 excretion. Of the contents of the pollen-tube, the larger part is again 

 excretion-substance. 



In the higher types it would appear as if the excretion of proto- 

 plasm from the female cell before impregnation had for its object 

 simply to form a nidus for the reception of the male fertilizing agent. 



Hybrid-pollination.* — Prof. E. Strasburger describes the con- 

 ditions under which it is possible for the pollen-grains of one species 

 to germinate on the stigma of another species, and the pollen-tubes 

 even to reaoh the ovules. Special contrivances to prevent the access 

 of foreign pollen are unnecessary, since pollen of the same species 

 always has an advantage over foreign pollen. Hybrids are com- 

 paratively very rare in nature, even in those species which display 

 the greatest tendency to hybridization. 



Latlujrus montamis will put out pollen-tubes which will reach to 

 the ovary of Convallaria latifolia ; and those of Agapanthus umbellatus 

 will penetrate deep into the style of Achimenes grandijiora. Those of 

 Fritillaria persica will not only enter the ovary of species of Orchis, 

 but will even excite the development of the ovules and will cause them 

 to begin to swell. The pollen-grains of Achimenes grandijiora will 

 not, on the other hand, penetrate the stigma of Agapanthus. 



The possibility of the pollen-grains of one species or genus 

 developing tubes on the stigma of another species or genus does not 

 depend on the possibility of hybridization between them. Orchis 

 Morio produces no pollen-tubes on 0. fusca, while, on the contrary, 

 the pollen-tubes of the latter enter the ovary of the former species, 

 cause the normal development of ovules, and occasionally even im- 

 pregnate them. As a rule, the pollen tubes penetrate into the style 

 or even the ovary to a depth proportional to the relationship of the 

 species, though this is not without exception, as in the case of 

 Lathyrus montanus and Convallaria latifolia, and therefore cannot be 

 regarded absolutely as a measure of sexual affinity. 



That varieties of the same species exhibit greater capacity for 

 exciting the development of pollen-tubes than species of the same 

 genus, depends simply on a greater resemblance in the composition of 

 the nutrient material furnished to the pollen-grains and tubes by the 

 stigma and style. Hybridization is an evidence of sexual affinity, 

 while its non-occurrence is no evidence of the absence of affinity. 



Unisexual Flowers and movements of the Stamens in Anemone.t 

 — Dr. S. Calloni states that it is quite common, towards the end of 

 March or beginning of April, to find flowers of Anemone hepatica 

 which have become unisexual by the complete suppression of the 

 stamens, and distinguished at once from the hermaphrodite flowers by 

 theii' small size. He also observed a slow motion of the stamens in 



* Versamml. Deutsch. Naturf. Strassburg, 1885. See Bot. Centralbl, xxiv. 

 (1885) p. 285. 



t Arch. Sci. Phys. et Nat., xiii. (1885) pp. 109-14. 



