FERTILIZATION OF FLOWERS. 368 



along its length. There are five petals, but only four are fully 

 developed, and these spread themselves out in the form of a 

 cross around the mouth of the tube in which the honey is 

 secreted. The anthers and stigma are borne on the end of a 

 long slender column which springs from the middle of the flower. 

 Close to its base the column is bent downwards at a sharp angle 

 so that it hangs out at one side of the flower, between two of 

 the fully developed petals and resting upon the aborted petal as 

 on a cushion. Near its apex the column is again bent at a sharp 

 angle, this time upwards. The flowers are protandrous, the 

 anthers becoming mature and shedding their pollen before the 

 stigma is fully developed. 



An insect, visiting the flower and poking its proboscis down 

 the tube of the corolla in search of honey, must touch the column 

 at the first bend. This is the irritable spot, and no sooner is it 

 touched than the column springs over to the other side of the 

 flower and brings the anthers or stigma, as the case may be, 

 down on the back of its visitor. In this way pollen is deposited 

 upon or removed from the insect's back and cross-fertilization is 

 effected. One of the most curious things about this case is that 

 the column loses its irritability at nightfall and refuses to jump, 

 however much you may ticlde it. 



The few examples of entomophilous flowers which we have now 

 studied must suffice to give some idea of how wonderfully minute 

 and perfect may be the adaptation of plants to highly specialized 

 environmental conditions. The dominating factor of the envi- 

 ronment here is, of course, the presence of insects, which can be 

 pressed into service as pollen carriers, and it is obviously in 

 relation to the requirements and tastes of these insects that the 

 various adaptations which we have been describing have arisen. 

 There can be little doubt that the insects select for their visits 

 those flowers which please them best and which are most readily 

 recognizable as the bearers of the coveted honey. 



Although, as we have previously pointed out, some carrion- 

 feeding flies prefer scents which are repulsive to ourselves, yet 

 the vast majority of insect-fertilized flowers have scents and 

 colours which we appreciate perhaps no less than the insects for 

 whose gratification they primarily exist. As we shall see later on, 

 these scents and colours, though now in many cases improved 

 by human selection, doubtless arose in the first instance in 

 response to insect selection. If we pursue this line of thought a 



