166 BOTANICAL GAZETTE [February 



Observations on Welwitschia — Pearson has communicated further studies 

 on this peculiar genus to the Royal Society, London, of which the following is an 

 abstract. 



* 



Macrospores and embryo sacs are frequently present in the pith region of 

 the female cone-axis. This confirms the view, already adopted by most authors, 

 that the ovule of Welwitschia is cauline. Sporogenous cells have not been 

 found in a similar position in the male cone. 



It is suggested that the female cone and the male flower are derived by reduc- 



that of Bennettites. 



type 



At the end of the free nuclear division the embryo sac contains about 1024 

 nuclei which are equivalent in all visible characters. Cleavage of the cytoplasm 

 occurs, resulting in the septation of the whole sac into compartments. Those 

 near the micropylar end contain few nuclei which are functionally sexual; most 

 of those of the lower three-fourths inclose many potentially sexual nuclei. The 

 former send out embryo-sac tubes into the nucellar cone and into them pass the 

 cytoplasm and free nuclei; all the nuclei in each of the latter fuse so that each com- 

 partment becomes a uninucleate cell. The compartments containing the fusion 

 nuclei form the primary endosperm, whose later growth is distributed over two 

 periods, one before and the second after fertilization. The endosperm of Gnetum 



is probablv formed in the samp vav T™ ~-~-~** ^ *u ^o^i^Voi rtiararter 



rm 



7 



m wmoi tne endosperm is a prothallus of the normal gymnosperm type. It is sug- 

 gested that the endosperm of the primitive angiosperms was homologous with that 

 of \\ ehvitschia. 



The embryo-sac tubes meet the pollen tubes in the lower half of the nucellar 

 cone. Fertilization occurs within the generative cell, which enlarges after leaving 

 the noil™ «,«. „ nd ; ts nucleus ^ vides The daughter nude i a re functional 



Several oospores are commonly formed in each nucellus. The cytoplasm of 



mfr1^T« re ^ S J n *i nly ' lf ^ entirdy ' P rovided b y the generative cell. A resting 



The oospore e i onRates toward the top f t he endosperm. 



— ~— ~- ^vision within it is followed by the formation of a centripetally 

 developed wall which separates the upper "primary suspensor" from a lower 

 terminal cell. From the latter are developed: (a) 24 cells which, surrounding the 



poll 

 gametes. 



formed 



. form 

 terminal irronn inrlnc;™ „ 1 



The 



toter stages f embryo development have not been seen; they possibly occur, as in 

 Gnetum, after the seed is detached from the plant. 



It is suggested that (1) the Gnetum- Welwitschia alliance has its origin in 

 the same stock as the angiosperms, but separated from the angiospe™ Hne 

 before the carpel became the pollen- receiver; (2) Welwitschia is the most special- 

 ized hvmg representative of the race to which it belongs. 



