46 SUMMARY OF CURRENT RESEARCHES RELATING TO 



three ovules, each subtended by a sporophyll. Soon after pollination 

 the pollen-grain divides into antheridial cell and tube-cell ; in J. com- 

 munis the former does not divide until the following April, while in 

 J. virgmiana it divides in the same year and fertilisation takes place 

 in June or July. The generative cell and the stalk-cell pass into the 

 tube, and the nucleus of the stalk-cell comes to lie near the tube 

 nucleus. When the pollen-tube has reached the archegonia, and just 

 before fertilisation, the generative cell divides to form two similar 

 hemispherical sperm-cells. The macrospore mother-cell appears one 

 year after pollination, and the first mitosis is heterotypic. The female 

 prothallium develops, as in other Gymnosperms, by free cell-formation. 

 The archegonia] group arises from superficial cells at the micropylar end 

 of the prothallium, and the group is surrounded by sheath-cells. On 

 the same day that the generative cell divides, the central cell of the 

 archegonium divides, but the ventral canal nucleus disintegrates without 

 forming a separate cell. It appears that Juniperus is of more modern 

 origin than many other Gymnosperms. 



Ovule, Gametophytes and Embryo of Widdring-tonia.* — W. T. 

 Saxton publishes a preliminary account of the life-history of Widdring- 

 tonia cupressoides, and the chief facts cited are as follows : — The genus 

 Widdringtonia is quite distinct from both Gallitris and Tetraclinis. 

 The male gametophyte is the most reduced type known among the 

 Gymnosperms, and no division of the microspore takes place until after 

 pollination. Many megaspores are formed, but only one forms a 

 prothallus, the early development of which is perfectly normal. Over 

 fifty archegonia are formed, and these are arranged in groups upon the 

 upper half of the prothallus, near the margin and on the side down 

 which the pollen-tube grows. Jacket-cells are poorly developed or 

 absent, and the archegonia are apparently without neck-cells. The 

 central nucleus of the archegonium gives rise to the egg nucleus and a 

 ventral nucleus. By karyokinesis the prothallus-cells become binucleate 

 or multinucleate, and this condition is persistent. The haploid number 

 of chromosomes is six and the diploid number twelve. Probably two 

 archegonia are fertilised by two sperms from one pollen-tube. The 

 development of the embryo is normal, and a resemblance to -that of 

 Sequoia sempervirens is to be noted. The details of development 

 indicate an approach to those of the Gnetales, especially Tumboa 

 {Welu'itschia). 



Embryo-sae of Smilacina stellata.f— F. McAllister has studied 

 the embryo-sac of Smilacina stellata, and finds that the mother-cell 

 divides to form four nuclei, separated by walls to form four megaspores, 

 but that owing to absorption of these walls, the four nuclei occupy a 

 common cell-cavity. By division eight nuclei are formed, which sub- 

 sequently organise to form the embryo-sac. Thus four megaspore cells 

 combine to form one embryo-sac or gametophyte. This seems to 

 suggest that in the embryo-sac of the Lilies the first four nuclei are 

 really megaspores. 



* Bot. Gaz., xlviii. (1909) pp. 1G1-78 (1 pi. and 3 figs.). 

 f Tom. cit., pp. 200-15 (1 pi.). 



