350 
ON CROSSES AND 
fancied that its successive applications in such cases made 
the seeds more numerous and perfect, which is very probable; 
but he says that only in kinds very closely allied did he 
obtain the full complement of seeds, as for instance in the 
genus Datura, of which Metel and Lsevis mix freety. He 
found the life of the stigma more prolonged, when it was 
not fertilized by its own pollen ; which might be expected, 
because the complete saturation of the stigma had not taken 
place, after which it no longer receives the influence of the 
pollen. He states that in natural fecundations the change 
of the stigma took place sometimes in 85 or 100 minutes, 
usually in a few hours, at most in 24 ; but neither he nor any 
other person seems to have thought of ascertaining whether 
the influence of the pollen really fertilizes the germen within 
that period, or merely saturates the stigma; and, although I 
have not pursued a course of experiments to make that fact 
sure, I have some reason to believe that the truth is not yet 
ascertained. If the fertilization was complete, and the office 
of the stigma defunct, it might be cut off without any detri- 
ment; unless necessary to the mere nourishment of the ovules, 
whether fertilized or not, which does not seem probable ; but 
I have repeatedly cut it ofl' a few days after I had applied 
pollen to Rhododendron, and the result has been that no seed 
has been formed. The whole of my observations has led me 
to think, that at any period before the decay of the stigma 
the access of the natural pollen may supersede the influence 
of the foreign that may have been previously applied, if not 
from a closely allied species or variety ; but that on the other 
hand no foreign pollen can act upon the germen after the 
stigma has been fertilized naturally. The incomplete satu- 
ration of the stio-ma in the first case enables the natural 
O 
pollen to gain access ; but, if the absorption of the pollen 
first applied causes immediate fecundation, it cannot be ex- 
plained how the subsequent access of the natural dust should 
supersede it ; and it has seemed to me that the natural pollen 
could supersede that of an Azalea on the stigma of an ever- 
green Rhododendron even after the flower had fallen off. 
This point, which I have not sufficiently investigated, might 
be elucidated by cutting off the stigma with portions of the 
style of various lengths at different periods after the applica- 
tion of pollen, and seeing in what manner the operation in- 
terferes with the fructification of the plant. Gaertner thinks 
it doubtful whether the corolla is essential to the fertilization 
