POLLEN STERILITY IN RELATION TO THE GEOGRAPH- 
ICAL DISTRIBUTION OF SOME ONAGRACEAE’ 
Cart C, FORSAITH 
(WITH PLATES XIX-XXI AND ONE FIGURE) 
Before the development of methods of research in biology, 
the question of the origin of species was not debatable, since it 
was taken for granted that all had arisen as a result of special 
creation. LINNAEUS, however, in 1757 was convinced that this 
doctrine needed modification. His departure from the accepted 
hypothesis was brought about by the appearance of an intermediate 
form of Tragopogon resulting from a cross of T. pratensis and T. 
porrifolius, to which he gave the significant species name T.. hybridus. 
Too much emphasis cannot be laid upon this fact, since it paved 
the way for the later and more complete conception of the funda- 
mental laws of evolution. 
From that time the occurrence of hybrid forms was recognized 
now and then, until the reality of their existence became uni- 
versally admitted. During the later investigations of these plants, 
it became evident that hybridism was very closely correlated with 
that of a more or less sterile quality of the generative organs, in 
proof of which there has arisen a prodigious amount of literature. 
These numerous citations may well be considered as having estab- 
lished the general biological principle of sexual impotency resulting 
from earlier parental crosses. Since this form of degeneration is 
observed more readily in the microspores than in the megaspores, 
it naturally follows that the presence of a large and varying amount 
of infertile pollen may be considered as indicative of previous inter- 
breeding of plants where such conditions obtain. Although this 
relation of pollen abortion to hybridism has become quite widely 
accepted, there appears to be still some doubt as to the validity of 
the general principle. Consequently, it may be advisable to 
mention a limited number of references in its support. 
* Contributions from the laboratories of Plant Morphology of Harvard Uni- 
versity No. 81. 
Botanical Gazette, vol. 62] [466 
