OF CAMPANULA. 603 
pollen, and 1 have seen them in different points of their pro- 
gress towards the cavity below. In the cavity itself I have 
also ascertained, by careful dissection, that three grains of 
pollen find for themselves a convenient receptacle. It is in 
the form of an oblong cylindrical cell, whose diameter is that 
of the grain of pollen, and its axis directed obliquely down- 
wards towards the axis of the style. It is about one-third as 
long as the exserted part of the tubular hair. It seems a 
just inference to assume that the pollen has entered by the 
foramen at the summit of the hair, during a momentary en- 
largement of the orifice specially adapted to this end. Those 
hairs only which are situated near the summit of the style 
have hitherto been found perfect in their office; but all of 
them are equally retractile ; some of the perfect ones are tu- 
midin the middle, so as to be spindle-shaped; in this case 
the inner tube is not distended beyond its ordinary size. 
The invagination of the pollen-collectors appears to be 
simultaneous with the act of fecundation, and may be com- 
pared to the peristaltic motion of the intestines of animals. 
It seems to be specially designed for the safe and sure con- 
veyance of the grains of pollen into the cavities which, as 
already stated, are formed in the substance ofthe cellular 
tissue of the style, where there is no visible impediment to 
the formation of pollen-tubes. Escept actual proof of the 
fact, I have every reason to think that this formation does 
take place, and that the impregnation of the ovules is ef- 
fected by this channel, and not by the necessary intervention 
of the stigma ; for it must be remarked that the branches of 
the stigma do not expand until some time after the pollen has 
been lodged upon the pollen-collectors, whence there is no 
visible means of conveying the pollen upwards into direct 
contact with the stigma, and it is quite a rare circumstance 
to find a stigma in any stage with pollen adhering to it. I 
leave this part of the subject to future inquiry, and proceed to 
notice the hairs in their invaginated state. They do, indeed, 
as Brongniart has well observed, withdraw themselves so 
