ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
767 
male and female organs in flowering plants, and of the details of the act 
of impregnation. The power of germination of pollen-grains was 
found to endure from one day in Oxalis Acetosella to eighty days in 
Narcissus pseudo- Narcissus. Light has a very prejudicial influence on 
the growth of the pollen-tube. 
The origin of the embryo-sac in different plants is stated as follows : — 
In Tulipa and Lilium it is derived directly from the hypodermal axial 
apical cell. In Cornucopise nocturnum, this cell divides into two unequal 
daughter-cells, of which the subapical again divides into two, and of 
these the lower becomes the embryo-sac. In Yucca gloriosa the division 
of the original apical cell is somewhat more complicated ; but again 
the lowest segment grows into the embryo-sac. In Clematis cirrhosa and 
Cercis siliquastrum the embryo-sac is again developed from the lowest 
segment. In the Gamopetalse the hypodermal axial apical cell divides 
into either three or four mother-cells, of which the lowest becomes the 
embryo-sac. 
With regard to the actual process of impregnation, the author agrees 
with Guignard rather than with Strasburger, and states that an actual 
fusion takes place of the male and female nuclei, the nucleoles present 
in both of them disappearing at the same time. 
Cleistogamic Flowers.* — Herr W. Burck describes several species 
of tropical plants which produce cleistogamic flowers, in which cross- 
pollination is impossible, although the flowers are coloured and scented, 
and produce abundance of nectar. This is the case in a number of 
species of Anonacese. In Myrmecodia, the explanation appears to be 
afforded by the hypothesis that the flowers were originally adapted for 
cross-pollination, but that the visits of insects have been gradually 
suspended in consequence of the attacks of the warlike ants which 
always inhabit the tubers. In Unona sp. nov. the corolla remains 
always completely closed, and yet abundance of fruit is produced. 
Importance of Heterogamy in the formation and maintenance of 
species.^— Commenting on Herr Burck’s paper, Herr F. Rosen argues, 
from the phenomena connected with cleistogamic flowers, and others 
in the vegetable kingdom, that cross fertilization does not play so impor- 
tant a part in the maintenance of species as has been supposed by most 
recent writers. Even with many anemophilous plants, such as Carex 
and Festuca , inbreeding appears to be the rule. 
Fertilization of Lilium Martagon.J — Dr. E. Overton finds this plant 
a very favourable one for following out the development and coales- 
cence of the sexual elements. The sculpturing of the mature pollen- 
grain is caused by short crowded rods ; these are wanting in a narrow 
longitudinal band which is but slightly cuticularized, and through which 
the pollen-tubes penetrate. The number of threads in the nucleus of 
the pollen-grain is twelve in the great majority of cases, though in a few 
instances the number was undoubtedly less. The pollen-tubes are 
directed to the canal of the style by means of the bicellular stigmatic 
* Ann. Jard. Bot. Buitenzorg, viii. (1890) pp. 122-64 (4 pis.). 
f Bot. Ztg., xlix. (1891) pp. 201-11, 217-26. 
j ‘ Beitr. z. Kenntniss d. Entwickelung u. Vereinigung d. Geschlechtsproducte b. 
Lilium Martagon ,’ Zurich, 1891, 11 pp. and 1 pi. 
