172 THE STRUCTURE OF FLOWERS. 



"II etait done evident que les parasites avaient determine 

 les memes effets que les tubes polhniques : raccroisement des 

 ovaires et des placentas et le developpement des ovules." 



The reader will here see the importance of this curious 

 instance as hearing upon my general theory of growth m' 

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

 can be stimulated into growth and development, there is 

 no d priori I'eason 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 tobe the case in Clerodendron* 

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



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

 action of the suspensor in Orchids, described by M. Ti^eub, 

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

 then ramifies in various ways, clasping and bui^rowing 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 organs of Orchids as accounting for the well- 

 known difficulty in raising seed from them : " Malgre le 

 nombre immense des grains formees dans les conditions' 

 naturelles comme dans les serres, nombre qui parait etre 

 d'ailleurs une signe de degradation physiologique dans une 

 famille ou la differenciation morphologique des organes floraux 

 est cependant si elevee, I'insuffisance de reserve alimentaire 

 contenue dans leur embryon microscopique, en necessitant des 

 conditions speciales pour le developpement, suffit peut-etre a 

 expliquer les difficultes et les insucces de la reproduction des 

 orchidees par gTaines, et la parcimonie relative avec laquelle 

 elles sent distribuees dans la nature." 



♦ See p. 130. t See p. 114. 



;J; Notes sur VEmbryog^nie de quelques Orchidees, Verhandelingen der 

 Koninklijke Akadamie van Wetenschappen, 1879. 



