474 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
tlie nuclei of the antipodals differ in their chromatophily from the other 
nuclei of the embryo-sac. Among Gymnosperms there is, in Biota, no 
difference in the size, structure, or chromatophily of the male nuclei, 
while they are still in the pollen-tube before impregnation. In Angio- 
sperms the male nucleus of the pollen-tube becomes, in contrast to 
the vegetative nucleus, cyanophilous at the moment of impregnation. 
The nuclei of the antipodals contain also a larger number of chromo- 
somes than the synergids or the oosphere. The erythrophily of the 
endosperm-nuclei disappears slowly on further segmentation. 
The author is disposed to attribute the difference in the chromato- 
phily of the pollen-nuclei to differences in their nutrition ; the erythro- 
philous nuclei containing a larger quantity of the (erythrophilous) 
nucleo-hyaloplasm than the cyanophilous nuclei. He also lays stress 
on the differences in the morphological structure of the two kinds of 
nucleus, especially in that of their framework. 
Physiology of Pollen.* — Prof. H. Molisch states that the pollen- 
grains of many plants (Compositae, Umbelliferae, Malvaceae, Urticaceae) 
will germinate only in contact with the stigma ; others will germinate 
in pure water ; others again in a solution of sugar, the concentration of 
which may be as high as 40-50 per cent. The pollen-grains of Ericaceae 
will not germinate in pure water, nor in a solution of sugar ; but they 
will in a 0*01 per cent, solution of malic acid, or in a 0*05-1*0 per 
cent, solution of calcium malate. The power of germination is re- 
tained, in different species, for a period varying from 12 to 72 days. 
The pollen-tube is either negatively aerotropic or indifferent to 
oxygen in the culture-fluid, never positively aerotropic. It is positively 
chemotropic to the secretion of its own stigma, and sometimes to that of 
the stigma of another species, even if not nearly related. This chemo- 
tropism must often have an important influence in directing the pollen- 
tube to the oosphere. 
The pollen-grain frequently contains starch. In most Compositae 
and in some other plants the membrane of the pollen-grain is partially 
composed of a substance which is coloured red-violet by concentrated 
sulphuric acid. 
Fertilization of Pinus. *f — Mr. H. H. Dixon reviews the results 
arrived at by Strasburger, Belajeff, and Overton, with regard to the im- 
pregnation of Gymnosperms. In the ripe pollen-grain of Pinus sylvestris 
there is a small prothallium-celi and a large nucleus, which is the 
nucleus of the pollen-tube, and passes into the tube which is formed 
immediately after pollination. The prothallium-cell remains attached 
to the wall of the pollen-grain ; and in this condition the pollen remains 
during the winter. The pollen-tube reaches the nucellus about thirteen 
months before fertilization takes place. 
Next spring the pollen-tube becomes filled with starch, and the pro- 
thallium divides to form a small pedicel-cell and a larger body-cell ; 
this latter then breaks away from the pedicel-cell and divides into two 
cells, which are the male sexual cells. These two male cells then move 
slowly down into the pollen-tube, closely followed by the nucleus of the 
* SB. K. Akad. Wiss. Wien, cii. (1893) pp. 423-48 (1 pi.), 
t Ann. Bot., viii. (1894) pp. 21-34 (3 pis.). Cf. this Journal, 1893, p. 756. 
