ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 433 



sac has divided into three superposed cells, the two upper of which 

 disappear and the lowermost developes into the embryo-sac ; in this the 

 sexual apparatus consists of a large oosphere and two synergidse with very 

 thin membranes. This apparatus is definitely constituted, in most of the 

 ovules, rather more than a month after pollination ; five weeks later impreg- 

 nation commences, and is completed in about a week. 



The pollen-grain has two nuclei, which are always found near the 

 extremity of the pollen-tube ; the hinder one, which is the generative 

 nucleus, usually divides into two. The tubes arrive at the base of the 

 cavity of the (jvary about twelve or fifteen days after pollination ; they 

 do not penetrate into the micropyle of the ovule until after the formation 

 of the sexual apparatus. 



In Vanda tricolor pollens the interval between pollination and fecunda- 

 tion is about six months ; in Angrsecum superhum about four months ; in 

 Phajus grandifolius two months ; in different species of Cypripedium from 

 tliree to four months ; in Saccolahium giganteum the ovular papillae have 

 not even made their appearance one month after pollination. In European 

 orchids the process is more rapid. In Orchis Mario there is an interval of 

 fifteen days ; in 0. latifolia three weeks ; in O. Simia thirteen days ; in 

 0. ustulata and pyramidalis eight to ten days ; in Gymnadenia conopsea 

 fifteen days ; in Ophrys arachnites three weeks ; in Limodorum ahortivum 

 twenty-five days. 



The pollen-tubes enter the ovary, through the conducting tissue of the 

 gynostemium, in six bundles, vrhich pass down the angle formed by each 

 placenta with the wall of the ovary, while the ovules are still quite rudi- 

 mentary. Contrary to the statement of Degagny,* he finds that many of 

 the tubes have transverse septa. 



M. Guignard confirms the observation of Van Tieghem,"]" of the produc- 

 tion by the passage of the pollen-tube of a kind of ferment, and regards the 

 development of the ovules as a kind of hypertrophy resulting from access 

 of abundance of nutriment. He compares it to the action on vegetable 

 tissues of such parasites as Synchytrium and JBlasmodiophora. 



Fertilization of Verbascum.| — M. P. Maury has closely examined the 

 mode of pollination and impregnation in several species of Verhascum, as 

 well as the development of the stamens. The formation of the anther- 

 lobes and of the mother-cells of the pollen-grains occurs at a very early 

 period. Pollination takes place at the moment of the dehiscence of the 

 anther ; but, all the species being decidedly proterandrous, the mode of 

 fertilization is indirect or entomophilous. The most remarkable fact 

 connected with impregnation, is that, at the period of pollination, the 

 ovules are still in a rudimentary condition, and altogether unfit for fertili- 

 zation. The nucellus is entirely occupied by the embryo-sac, in the 

 protoplasmic contents of which there is as yet no diiferentiation of 

 oosphere, synergidse, or antipodals. It is only after the pollen-tube 

 reaches the micropylar canal that these begin to be formed. There being 

 no nectary in any species of Verhascum, insects appear to be attracted 

 mainly by the coloured hairs attached to the filaments and by the striae at 

 the base of the corolla. 



Fertilization of Greenland Flowers.§ — Prof, E. Warming has examined 

 the flora of Greenland between lat. 64° and 69° 15', especially from the 



* See this Journal, 1885, p. 273. t Ibid., ante, p. 273. 



X Bull. Soc. Bot. France, viii. (1886) pp. 529-36. 



§ Overs. K. Danslic Videusk. Selsk., 1886, pp. xxv.-xsxiii. (French re'sume'), and 

 101-59 (13 figs.). 



