124 STRUCTURAL BOTANY 



mere "shock" of the operation which pi events the 

 seeds from ripening, for if pollen from another flower 

 be placed on the stigmas of the mutilated flowers 

 their seeds will ripen in due course, and when they 

 are sown the embryos will grow into young plants as 

 usual. 



We learn, then, that the access of pollen to the 

 stigma is a necessary condition for the formation of 

 fertile seeds. It was by experiments of this kind, per- 

 formed about two hundred years ago, that the existence 

 of distinct sexes in plants was first proved. We now 

 know that the function of the flower is the sexual re- 

 production of the plant. We are thus in a position 

 to study in detail how the process goes on. 



In plants like the Wallflower, which have con- 

 spicuous, brightly-coloured, and sweet-smelling flowers, 

 the work of pollination is chiefly performed by insects, 

 The Wallflower is specially attractive to bees, who 

 visit it in search both of honey and of pollen, the " bee- 

 bread," which is collected as food for the young brood. 

 The bees are quite as useful to the Wallflower as the 

 Wallflower is to the bees, for in the course of their 

 visits they do it the essential service of bringing the 

 pollen on to the stigmas of its flowers, and so ensuring 

 fertilisation. We have already seen that there are 

 two large honey-glands or nectaries in the flower. 

 The honey formed by these glands collects in the 

 pouches of the inner sepals. As the bee thrusts her 

 proboscis down between the stamens and the pistil in 

 order to reach the honey, her head comes into contact 

 with the inner side of the anthers, on which a mass 



