126 ANATOMY AND PHYSIOLOGY OF 



Observ, As the minute exposition of tlie historical development of the 

 theory of the sexes of plants would occupy far too large a space, an indi- 

 cation of the mam points mu.&t suffice. Although the cultivation of 

 many monoecious and dioecious plants might have led, even m ancient 

 times, to the idea that plauts were fui-nished with sexual organs of two 

 kinds, this ti'uth was not recognized until towards the end of the 17th 

 century. First announced m England by Grew, Eay, and others, this 

 theory obtained its first scientific establishment from E. J. Camerarius of 

 Tubingen (''Be seoou plantarum epistola,'' 1G94); but it was Linnaeus more 

 especially who securely established this new theory by his researches, and 

 gave it universal diffusion by the preponderating influence he exercised in 

 Botany, and by the displacement of all earlier systems by his Sexual System. 

 When, finally, Kolreuter, succeeded by a longer series of experiments in 

 demonstrating the possibility of producmg Hybrids in the Vegetable King- 

 dom (" Vorlauf. Nachricht einig. d. Geschlecht d Pflanzen letreff. Versuche" 

 1761 — 1766), the theory of the sexuality of plants was as firmly establish- 

 ed as it could be without a knowledge of the changes which the pollen- 

 grains undergo upon the stigma and the processes occurring in the 

 ovule. The last century did not essentially advance further in reference 

 to this point. The excellent researches of Malpighi, if not forgotten or 

 mismiderstood, were at all events not completed ; as to the structure and 

 characters of the pollen and as to its relations to the stigma, numerous in- 

 correct observations were published. "With this imperfect knowledge of 

 the processes occurring in the interior of the ovule, it might easily be 

 thought possible that fertile seeds should be perfected, at all events, in 

 particular cases, without the co-operation of the pollen, and a number 

 of observations were made known, partly in favour of such exceptional 

 cases, and partly with the object of refuting the entke theory of the sexes 

 of plants } thus Spallanzani and others asserted that female specimens of 

 Hemp, Spinage, &c., had borne fertile seeds; Henschel beHeved that 

 road-dust, powdered charcoal, sulphur, &c., might be substituted for the 

 pollen ; Schultz stated, as the result of his observations, that the pollen 

 need not necessarily come in contact with the stigma, but might impreg- 

 nate from a distance by an aura seminalis ^ and Lecoq thought he had 

 found that fertile seed might be developed without application of pollen 

 to the stigma in monocarpic, but not in polycarpic, plants. The doubts 

 thus excited were set at rest for ever by the brilliant discovery of 

 Amici, that the pollen- grains germinate upon the stigma and that their 

 internal coat grows down in the form of a tube through the style 

 into the ovary, and comes into connection with the ovule (1823 — 

 1830) ; a discovery to which Gleichen had already come very near, 

 but had not properly followed out. The universality of this process 

 has indeed been denied, l3ut day by day the opposition becomes more 

 completely silenced. Parallel with the researches on the structure of 

 the pollen and its relation to the stigma, went the investigations on the 

 ovule and the origin of the embryo, which had been taken up again from 

 the last-mentioned period by Treviranus, and subsequently carried out 

 fui-ther by Eob. Brown, Brongniart, Mirbel, Schleiden, Hofmeister and 

 others. In the midst of this new development of the theory of impregna- 

 tion, not the sexuality, but the respective import of the sexual organs, 

 was unexpectedly called in question, by Schleiden stating that he had disco- 



