THE MAKING AND UNMAKING OF FLOWEKS. 119 



It Will be noticedjthat these shrubs have opijosite and not alternate leaves, 

 as on the Oak, so that they are not arranged spirally. Hence they have, 

 presumably, given rise to flowers having their whorls made up of pairs of 

 parts. Thus the Lilac is composed as follows : Calyx, 4 ; corolla, 4 ; 

 stamens, 2 ; carpels, 2. Monocotyledonous plants, as a rule, have the 

 floral whorls'ini threes^ (fig. 44). This appears to be due to the fact that 

 the leaves on the stems are so arranged that the fourth leaf, when traced 

 up on a spiral line, falls over the one chosen as No. 1, so that three leaves 

 make a cycle, and therefore a whorl. 



Before - we proceed any further it will be as well to ask : What has 

 brought about the changes referred to thus far ? It is a fundamental law 

 of evolution that nothing is made originally in anticipation of a- future use. 

 There must be an external inciting cause, to which the flower responds 

 and builds up the adaptiv e structures, and then it may become hereditary 

 and be reproduced in every subsequent generation in anticipation of its 

 use. 



The stimulating cause in the case of flowers adapted in their structure 

 for insect fertilisation is the actual visit of the insect itself, when searching 



Fig. 44. — Diagram of flower of Iris. Fig. 45. — Vertical section of flower of 



Strawberry. 



for pollen first, and for honey afterwards, i.e. in the evolutionary history of 

 flowers. 



If we go back to Gymnosperms again, in all existing species the sexes 

 are distinct, either on the same tree (Fir) or on difl:"erent trees (Yew). 



In the absence of pollen-eating insects, the only way the ovules could 

 be fertilised and ripen into seed is by the wind blowing the pollen on to 

 the exposed ovules. 



Now, when insects visit honeyless flowers for the sake of pollen it has 

 been observed that they constantly probe the juicy floral receptacle in 

 order to moisten the pollen. H. Miiller noticed bees so doing, for example, 

 in the flowers of the Wood Anemone, &c. 



Here, then, we have the first source of "floral irritation." We know 

 of no other, but when we come' to speak of irregular flowers we shall see 

 what a number of coincidences there are in the various structures of such 

 flowers, all of which conspire to secure one and the sanu^ end ; so that the 

 conclusion is irresistible that it is the insect itself which has incited the 

 plant to build up a flower in perfect response both to tlie insect's and its 

 own requirements. 



