22 HBTBROSTYLBD DIMORPHIC PLANTS. Chap. I, 



tilised 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 mus- 

 corum, 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 Cucullia verhasei 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 

 pollen being deposited on it. It follows from the 

 position of the organs that if the proboscis of a 



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

 phora pilipes and a Bomhylius Dec. 10th, 1874, p. 111. 



