BIOLOGY OF THE FLOWER 



175 



pollen, much of which is wasted. Flowers possessing a 

 perianth may have only a single whorl, and this is often 

 petaloid. In those with a double perianth a calyx 

 and a corolla the latter is usually attractive. In the 

 lower types the parts are free, the flower-cup is more or 

 less open, and the pollen and honey are very accessible 

 to insects. In vaiious ways, however, a flower-tube is 

 developed in higher forms which protects the honey 

 from rain and excludes the lower types of short-tongued 

 insects. 



We have now to consider a 

 further stage in the development 

 of the flower-tube and its relation 

 to the habits and structure of the 

 higher and more intelligent types 

 of insects. 



Tubular flowers with united petals. 

 The Cross-leaved Heath has five 

 united sepals and five petals joined 

 by their edges to form a tube ; 

 the corolla is thus gamosepalous. 

 Within the bell-shaped corolla (Fig. 

 120) are the stamens, which are 



peculiar. Each anther has two long processes or arms, 

 and these project outwards towards the corolla- wall. Near 

 the top of each anther are two pores, through which the 

 pollen escapes when ripe. The pistil is superior and 

 syncarpous, and around its base is a ring-like nectary ; 

 the style is long and projects beyond the anthers to the 

 mouth of the bell. An insect visiting the flower will 

 bring its head against the stigma and, in pushing its 

 proboscis into the flower to obtain the honey, touch the 

 anther-processes, which, acting as levers, will separate the 

 anthers and cause a shower of pollen to fall on to 

 the head of the insect. The tube is too deep for the 



sh 



Fig. 120. Flower of 

 Cross-leaved Heath. 

 Pr, anther-processes ; st, 

 stigma. 



