482 BOTANICAL GAZETTE [DECEMBER 
Conditions of spore formation very similar to those described 
for the 2 species of Gongylocarpus were observed in Zauschneria 
californica Presl. It was possible to obtain only 4 specimens, but 
those presented microspore development such as might readily be 
expected in a monotypic genus. All the pollen cells were equal 
in size and fertility, as indicated by figs. 17 and 18. Fig. 17 repre- 
sents a low magnification of the pollen of Zauschneria, and it will 
readily be observed that all the spores are perfectly developed. 
Fig. 18, a higher magnification, shows this fact even more conclu- 
sively. It is apparent also that all the spores in each tetrad reach 
maturity, and in no case do they show degeneration such as is 
habitual in 3 of the megaspores of the mother cell. 
In respect to spore formation, this genus shows features parallel 
to those presented by the essentially monotypic Gongylocarpus 
and the geographically limited Epilobium: angustifolium. ‘The 
presence of entirely fertile pollen in these species is very significant. 
It is evident, of course, that hybridism is impossible. On this 
account all the specimens under consideration may be regarded as 
representative of pure lines of descent. That this purity of lineage 
is closely related to a perfect development of the pollen cells is 
strikingly evident from studies in this direction. ‘The monotypic 
Zauschneria and the essentially monotypic species just cited gen-. 
erally present microspores which are perfect in every respect. 
Opposed to this type of spore formation, however, species possessing 
known or apparent hybrids generally contain pollen which is prone 
to abortion in varying degrees. Consequently, these 2 types 0 
kindred phenomena show in a very conclusive manner the validity 
of the assumption that sterile pollen is reliable proof of hybrid 
lineage. 
In the earlier paragraphs of this paper, the writer has attempted 
to show that there are certain general biological principles which 
have become firmly established. Naturally these principles have 
grown slowly, and have become far-reaching only in direct pro- 
portion to the amount of investigation carried on in relation to their 
application. Among the many laws thus formulated, that in 
regard to sexual impotency of hybrids is of the utmost importance 
in this discussion. The study of this problem, however, leads to 
