Imperfect Sporangia in certain Pteridophytes. 
Are they vestigial? 
BY 
F. O. BOWER, Sc.D., F.R.S., 
0 
Regius Professor of Botany in the University of Glasgow. 
I MPERFECTLY developed parts have played an im- 
portant role in arguments on Evolution. On the zoo- 
logical side especially they have been used as weighty 
evidence. Similarly, on the botanical side they have been 
the basis of discussion : in the morphology of the flower, 
abortive stamens, carpels, pollen-sacs, and ovules have been 
cited as foundations for elaborate comparative argument. 
For instance, where present in normal 'position the existence 
of an abortive stamen, or staminode, has been accepted as 
sufficient indication of the previous existence of a fully 
developed stamen in the ancestral line ; and on such evidence 
natural affinities have been traced and accepted, usually with- 
out question. 
But floral morphology has gone further : comparative study 
has led to the conclusion that in certain ancestral lines of 
descent parts have existed, which in the descendants of the 
present day are entirely unrepresented by any vestigial 
growth. This condition of complete disappearance of a part 
or parts has been styled ‘ ablast,’ as distinct from ‘ abortion,’ 
where the incompletely developed part has an objective exist- 
ence 1 . Against the former, as a fiction of Comparative 
1 These distinctive terms were introduced by Schmitz (Hanstein’s Bot. Abhandl., 
Bd. ii, Heft i, p. 57). 
[Annals of Botany, Vol. XV. No. LVIII. June, 1901.] 
Q 
