172 THE STEUCTURE OF FLOWERS. 



"II etait done evident que les parasites avaient determine 

 les memes effets que les tutes polliniques : I'accroisement des 

 ovaires et des placentas et le developpement des ovules." 



The reader will tere see the importance of this curious 

 instance as bearing upon my general theory of growth in 

 response to irritation ; so that if ovaries, placentas, and ovules 

 can he stimulated into growth and development, there is 

 no a priori reason why other parts of flowers may not equally 

 well grow in response to irritations set up by the insect 

 visitors ; as I have already shown to be the case in Clerodendron* 

 and in Mr. O'Brien's experiments.! 



Perhaps it will not be amiss to notice here a very similar 

 action of the suspensor in Orchids, described by M. Treub, 

 which grows "backwards," escapes from the micropyle, and 

 then ramifies in various ways, clasping and burrowing into 

 the ovarian walls like a parasite in order to convey nutritive 

 matters to the rudimentary pro-embryo. J 



Finally, M. Guignard remarks upon the degradations in 

 the essential oi'gans of Orchids as accounting for the well- 

 known difficulty in raising seed from them : " Malgre le 

 nombre immense des grains formees dans les conditions 

 natarelles comme dans les serres, nombre qui parait etre 

 d'aillenrs nne signe de degradation physiologiqne dans nne 

 famille ou la difEerenciation morphologiqne des organes floranx 

 est Dependant si elevee, I'insuffisance de reserve alimentaire 

 contenue dans leur embryon microscopique, en necessitant des 

 conditions speciales pour le developpement, snffit pent-etre a 

 expliquer les difficultes et les insucces de la reproduction des 

 orchidees par graines, et la parcimonie relative avec laquelle 

 elles sent distribuees dans la nature." 



• See p. 130. f See p. 114. 



t Notes aur V EmhryogAiie de quelques Orchidies, Verb&ndelingen der 

 Eoninkliike Akadamie van Wetenschappen, 1879. 



