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 

 Compositse; 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 

 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, 



>, 



I 



i 







* Kerner cleaTly shows that this 

 is the case : ' Die Schutzmittel des 

 Pollens/ 1873, p. 28. 



t 'Gardener's Chronicle/ 1861, 

 p. 1067. Lindley, 'Vegetable 

 Kingdom/ on Chrysanthemum, 

 1853, p. 706. Kerner in his inter- 

 esting essay ('Die Schutzmittel 

 der Bliithen gegen unberufene 

 Gaste/ 1875, p. 19) insists that the 

 petals of most plants contain mat- 

 ter which is offensive to insects, 

 so that they are seldom gnawed, 



and thus the organs of fructifica- 

 tion are protected. My grand- 

 father, in 1790 ('Loves of the 

 Plants/ canto iii. note to lines 184, 

 188), remarks that "The flowers 

 or petals of plants are perhaps in 

 general more acrid than their 

 leaves ; hence they are much sel- 

 domer eaten by insects/' 



X 'TJeber die Geschlechtsver- 

 haltnisse bei den Compositen/ 

 1869, pp. 78-91. 



