180 THE VEGETABLE WORLD. 
from opening, as was thought, on the stigma, in order to pour out 
the fecundating matter, changed by degrees into a sort of mem- 
branous tube, which he called the pollen-tubes, as represented in 
A, B, 0, Fig. 272, which shows the successive stages through which 
the pollen passes when the pollen-tube is thrown out at the moment 
of fecundation. 
In 1827 the celebrated botanist, M. A. Brongniart, in his 
researches on this subject, perceived that the same fact recorded by 
Amici occurred in numerous plants; he observed also that the 
pollen-tubes generally penetrated more or less into the style. He 
. instanced the Datura as one of those plants in which the action of 
the pollen on the stigma is very observable. ‘These tubular 
sacs,” he says, “are for the most part already filled with granules, 
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and easily distinguished 
from the tissue of the 
_ stigma by their brownish 
colour and opacity. 1 
could not find a better 
comparison for one of 
these stigmata,” he adds, 
“than a pincushion en- 
tirely filled with pins 
stuck into it up to the 
head.” 
Fig. 273 represents, 
according to the accoun 
of M. Brongniart, a ver- 
tical section of a stigma 
of Datura fecundated and 
furrowed with pollen 
tubes through all its 
thickness. Such is the 
appearance which the 
stigma of the Datura 
presents when strongly 
Fig. 274 is intended to show the same arrangement in the same 
plant, but still more strongly magnified. The grains of pollen 
