6 INTEODUCTION. 



however, are of service in another and very different 

 manner, namely, by folding inwards at night and 

 during cold rainy weather, so as to protect the florets 

 of the disc* Moreover they often contain matter 

 which is excessively poisonous to insects, as may be 

 seen in the use of flea-powder, and in the case of 

 Pyrethrum, M. Belhomme has shown that the ray- 

 florets are more poisonous than the disc-florets in the 

 ratio of about three to two. We may therefore believe 

 that the ray-florets are useful in protecting the flowers 

 from being gnawed by insects.f 



It is a well-known yet remarkable fact that the cir- 

 cumferential flowers of many of the foregoing^ plants 

 have both their male and female reproductive organs 

 aborted, as with the Hydrangea, Viburnum and certain 

 Compositee ; or the male organs alone are aborted, as 

 in many Compositse. Between the sexless, female and 

 hermaphrodite states of these latter flowers, the finest 

 gradations may be traced, as Hildebrand has shown. J 

 He also shows that there is a close relation between 

 the size of the corolla in the ray-florets and the degree 

 of abortion in their reproductive organs. As we have 

 good reason to believe that these florets are highly 

 serviceable to the plants which possess them, more 

 especially by rendering the flower-heads conspicuous 



* Kemer clearly shows that gnawed, and thus the organs of 



this is the case :' Die Schatzmlttel fouctifioatioa are protected. My 



des Pollens,' 1S73, p. 28. grandfather in 17il0 (' Loves of 



t ' Gardener's Chronicle,' 1861, the Plants,' canto iii. note to lines 



p. 1067. Lindley, 'Vegetable 184, 188) remarks that "The 



Kingdom,' on Chrysanthemum, flowers or petals of plants are 



1853, p. 706. Kerner in his in- perhaps in general more acrid 



teresting essay (' Die Schutzmittel than their leaves ; hence they are 



der Bliithen gegen linberufene much seldomer eaten by insects." 



Gitste,' 1875, p. 19) insists that J 'Ueber die Gesohlechtsver- 



the petals of most plants contain haltuisse bei den Gompositen,' 



matter which is offensive to in- 1869, pp. 78-91. 

 sects, so that they are seldom 



