22 HETEEOSTYLED DIMORPHIC PLANTS. Chap. 1 



cowslips of both forms, protected from insects in mj 

 greenhouse, did not set one pod, though artificially 

 fertilised flowers in other pots produced an abundance. 

 We thus see that the visits of insects are absolutely 

 necessary for the fertilisation of Primula veris. If the 

 corolla of the long-styled form had dropped off, in- 

 stead of remaining attached in a withered state to 

 the ovarium, the anthers attached to the lower part of 

 the tube with some pollen still adhering to them 

 would have been dragged over the stigma, and the 

 flowers would have been partially self-fertilised, as is 

 the case with Primula Sinensis through this means. 

 It is a rather curious fact that so trifling a difference 

 as the falling-off of the withered corolla, should make 

 a very great difference in the number of seeds pro- 

 duced by a plant if its 'flowers are not visited by 

 insects. 



The flowers of the cowslip and of the other species of 

 the genus secrete plenty of nectar ; and I have often 

 seen humble-bees, especially B. hortorum and muscorum, 

 sucking the former in a proper manner,* though they 

 sometimes bite holes through the corolla. No doubt 

 moths likewise visit the flowers, as one of my sons 

 caught CueulUa verbasci in the act. The pollen readily 

 adheres to any thin object which is inserted into a 

 flower. The anthers in the one form stand nearly, but 

 not exactly, on a level with the stigma of the other ; 

 for the distance between the anthers and stigma in the 

 short-styled form is greater than that in the long- 

 styled, in the ratio of 100 to 90. This difference is 

 the result of the anthers in the long-styled form 

 standing rather higher in the tube than does the 

 stigma in the short-styled, and this favours their 



* H. Miiller has also seen An- sucking the flowers. ' Nature, 

 thophora pilipes and a Bombylius Dec. 10th, 1874, p. 111. 



