CHAP.iv.J REPRODUCTION OF PLANTS. 133 



prolonged downwards into a hollow horn-like projection 

 or spur, also a nectary ; and in other plants belonging to 

 the same order there is a sequence in the evolution of 

 the nectary from the comparatively unprotected form 

 presented by the buttercup, which is accessible to insects 

 that cannot fertilize the flower, to the elongated spur- 

 like form that secures the nectar from being sipped by 

 insects that cannot fertilize the flower, and at the same 

 time making it more accessible to those long "tongued" 

 insects, as bees, etc., that can effect this object. But, 

 as already mentioned, insects adapt themselves to cir- 

 cumstances as well as plants do, and we find adventurous 

 ants and minute beetles that have a taste for nectar, but 

 cannot fertilize the flower, overcome the difficulty placed 

 in their way by the plant in secreting its nectar at the 

 bottom of a long slender tube or spur, by venturing 

 down the narrow passage. This defeat is in turn 

 remedied in many plants by a further modification of 

 parts ; in the violets the opening to the spur is guarded 

 by the growth of two slender spines from two of the 

 anthers that pass down into the spur, these completely 

 prevent the bodily entrance of any small insect, at the 

 same time leaving sufficient space for the slender tongue 

 of the insect specially adapted to effect fertilization. 

 The common red dead-nettle prevents the entrance of 

 minute insects to the honey situated at the bottom of the 

 tube^shaped corolla by the development of a ring of 

 hairs that grow from the inside of the corolla-tube and 

 meet in the centre. Some short-tongued bees that can- 

 not reach the honey situated at the bottom of a long 

 spur or corolla-tube have acquired the habit of biting 

 through the corolla-tube and sipping the nectar. In the 



