174 BOTANICAL GAZETTE [SEPTEMBER ; 
: 
(Welwitschia).s A consideration of this question and also of the — 
possible relation between the multinucleate prothallial cells of the 
two genera is better postponed, however, until PEaRson’s later 
researches on Tumboa have been published, and a closer series has 
been obtained in Widdringtonia.° : 
One interesting point, suggested by the fact that karyokinetic 
divisions occur in the prothallus at about the same time as the ventral 
nucleus is cut off, is that all the cells of the prothallus are potential 
archegonia. If the neck cells are really absent, the only essential 
difference between an archegonium with its egg and ventral nuclei : 
and the other binucleate cells of the prothallus is one of size. 
SUMMARY 
1. The genus Widdringtonia is quite distinct from Callitris and 
should be kept as a distinct genus, excluding Tetraclinis. 
2. A fixing agent not generally employed in cytological work 
has been found to give better results than chromacetic mixtures with 
and without osmic acid. 
3. The male gametophyte is of the most reduced type yet recorded 
in the gymnosperms, no division of the microspore occurring “ 
some time after pollination, and the tube and stalk nuclei disappeating 
before the body cell divides and before the archegonium initials can 
be recognized. 
4. A very large number of megaspores are probably formed, but 
only one of these ever forms a prothallus. 
5. The early development of the prothallus is perfectly normal. 
6. A very large number of archegonia (over so) are formed, and - 
these are arranged in a number of groups near the margin of the Pr 
thallus on the side down which the pollen tube grows. They are 
confined to the upper half of the prothallus (but absent from the 
apex). 
7. The archegonia arise from deep-seated cells of the prothallus 
and never grow through to the margin. 
3 See REN 4 arks (30) th t i f this remar 
kable plant. 
® Since the above was written, an abstract of PEARSON’s paper (29) has gone 
lished. He now finds the origin of the endosperm in Tumboa to be quite 
