the co-operation of the pollen is indispensable to the formation
of the embryo in the growing seed, and that plants therefore
have sexuality exactly as animals have it. Gärtner did not
content himself with simply making new experiments in fertilisation; he refuted the objections of Spallanzani, Schelver,
Henschel, Girou and others in detail from fresh experiments
and from other sources of information, paying particular regard
to all the circumstances which could come under consideration
in each case ; he exposed the inaccuracy of the observations of
the opponents of sexuality point by point, and finally called attention to a number of remarkable phenomena observable in the
ovary even before fertilisation, and to the circumstances under
which the pollen may find its way to it in cases where ordinary
pollination has been apparently prevented. These observations
once more confirmed the existence of sexuality in plants, and
in such a manner that it could never be again disputed.
When facts were observed in 1860, which led to the presumption that under certain circumstances in certain individuals of some species of plants the female organs might
produce embryos capable of development without the help of
the male, there was no thought of using these cases of
parthenogenesis to disprove the existence of sexuality as the
general rule ; men were concerned only to verify first of all
the occurrence of the phenomena, and then to see how they
were to be reasonably understood side by side with the
existing sexuality, as had to be done also in the corresponding
cases in the animal kingdom.
Gartner's work on hybridisation had been preceded by other enquiries into the same subject, those namely of Knight mentioned above at the beginning of the century, and Herbert's more ample investigations published in his work on Amaryllideae in 1837. Gärtner did not neglect to compare his observations at all points with the results of his predecessors, especially those of Koelreuter, and he deduced from the astonishing mass of material a number of general propositions
