6 INTRODUCTION. 



ing 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 

 Compositae; or the male organs alone are aborted, as 

 in many Compositae. 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 

 to insects, it is a natural inference that their corollas 

 have been increased in size for this special purpose; 

 and that their development has subsequently led, 



* Kerner clearly shows that this and thus the organs of fructifica- 

 is the case : ' Die Schutzmittel des tion are protected. My grand- 

 Pollens,' 1873, p. 28. father, in 1790 ('Loves of the 



t ' Gardener's Chronicle,' 1861, Plants,' canto iii. note to lines 184, 



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



Kingdom.' on Chrysanthemum, or petals of plants are perhaps in 



1853, p. 706. Kerner in his inter- general more acrid than their 



esting essay ( ' Die Schutzmittel leaves ; hence they are much sel- 



der Bliithen gegen unherufene domer eaten hy insects." 



Gaste,' 1875, p. 19) insists that the | 'TJeber die Geschlechtsver- 



petals of most plants contain mat- haltnisse hei den Compositen,' 



ter which is offensive to insects, 1869, pp. 78-91. 

 BO that they are seldom gnawed, 



