6 INTEODUCTION. 



kuwever, are of service in another and yery 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 sho\vii 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.t 



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 

 Compositae ; 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. | 

 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 



• Kerner clearly shows that gnfxwed, and thus the organs of 



tliisls the case :' Die Schutzmittel fruotitioatioii are protected. My 

 des Pollens,' 1S73, p. 28. ^ grandl'atlier in 17a0 (' Lores of 



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



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



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



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



terosting essay ('Die Subutzraittel than iheir leaves ; hence they are 



der Bliithen gegea unberufene much seldomer eaten by insects." 



Giiste,' 1875, p. 19) insists that J ' Ueber die Gesehlechtsrer- 



the petals of most plants contain haltnisse bei den Composilen,' 



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

 eeuts, so tliat tliey are seldom 



