wards through the style to the ovules, and are there either
hatched into embryos or assist in their production. This way
of conceiving the matter was closely connected with the theory
of evolution which then prevailed, and seemed to find some
countenance in the seed-corpuscles of animals; it was also
supported by the observation that pollen-grains placed under
the microscope in water often burst and discharge their con-
tents in the form of a granular mucilage. It has been already
mentioned that Koelreuter rejected this view; he declared the
bursting of the pollen-grains to be contrary to nature, and con-
sidered the oil which exudes from the grains to be the fertilising
substance. This view was adopted by Joseph Gärtner and
Sprengel, but it fell into disesteem, while that of Needham and
Gleichen commanded some assent some years longer. The
next question was, how the granular contents of the pollen-
grain reach the ovules. Accident supplied a starting-point for
further consideration. Amici, who was examining the hairs on
the stigma of Portulaca for another purpose, saw on that
occasion (1823) the pollen-tube emerge from the pollen-grain,
and the granular contents of the latter, commonly known as
the fovilla, execute streaming movements like the well-known
movement in Chara. The desire to verify this remarkable
fact, and to discover how the fertilising substance is absorbed
by the stigma, led Brongniart in 1826 to examine a great
number of pollinated stigmas. He succeeded in establishing
the fact that the formation of pollen-tubes is a very frequent
occurrence. The want of perseverance in following out his
observation and a prepossession in favour of Needham's old
theory prevented him from discovering the course of the
pollen-tubes all the way to the ovules ; he supposed, indeed,
that after penetrating into the stigma they open and discharge
their granular contents, and he maintained distinctly that these
are analogous to the spermatozoids in animals, and are the
active part of the pollen. But now Amici addressed himself
more earnestly to the question, and in 1830 he not only
Page:History of botany (Sachs; Garnsey).djvu/452
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432
History of the Sexual Theory.
[BOOK III.