468 2 BOTANICAL GAZETTE [DECEMBER 
discussion of a special case, he concludes as follows: ‘“‘Ce resultat 
m’apparait donc fournir un argument important en faveur de la 
nature hybride de la plante en question.”’ 
The advent of the mutation theory of DeVries added a new 
factor to this discussion, the results of which have appeared in 
numerous publications. A brief mention of a very few of these 
results in regard to the correlation of hybridization and sexual 
impotency will suffice. DrVriEs (7) speaks of reduced fertility 
in crosses of Oenothera biennisXmuricata and Cytisus laburnumX 
purpureus; BEER (4) showed that all the pollen of Oenothera longi- 
folia did not reach maturity, as there was not sufficient nutritive 
material to carry all the grains to completion; T1scHLER (23) 
described a Bryonia hybrid resulting from a cross of Bryonia alba 
and B. dioica thus: “Die Pollenkérner sind sehr haufig (bei 
Grecory fast immer) degeneriert, und von sehr ungleicher Grésse”’; 
and GaTEs (12, 13, 14) describes the cytological development in 
relation to pollen degeneracy in some hybrid species of Oenothera. 
Bateson (3) has been very influential in establishing the 
principle of sterility as a result of hybridism. Numerous references 
to his own observations add much weight to the value of the proba- 
bility that previous crossing is indicated by an important condi- 
tion of the microspores. This proof is augmented likewise by many 
citations of the results obtained by other investigators of this 
phenomenon. Conclusions similar to these were obtained by 
JeFFREY (18, 19, 20) as a result of studies of a large number of the 
vascular cryptogams, conifers, and angiosperms. ‘The results of 
his researches may be summarized briefly as follows. In the more 
constant and distinct species, the pollen grains are generally equal 
in size, full of protoplasm, and show no indications of an arrested 
development. On the other hand, those forms which show a large 
egree of fluctuation and contain known hybrids, generally present 
a varying amount of impotent pollen cells. ‘These opposing con- 
ditions are strictly in accord with the general principle just men- 
tioned. Consequently, JeFFREY was led to infer that those species 
which are characteristically constant and exhibit perfect pollen 
should be considered as pure. In contrast to this type of spore 
development, he regarded those forms which are habitually variable 
