11.] ARUM, ARISTOLOCHIA. 29 



As, however, in Aristolochia, so also in Arum, small 

 insects which, attracted by the showy central spadix, 

 the prospect of shelter or of honey, enter the tube while 

 the stigmas are mature, find themselves imprisoned, 

 by the fringe of hairs (Fig. 29, li), which, while per- 

 mitting their entrance, prevent them from returning. 

 After a while, however, the period of maturity of the 

 stigmas is over, and each secretes a drop of honey 

 thus repaying the insects for their captivity. The 

 anthers then ripen and shed their pollen, which falls 

 on and adheres to the insects. Then the hairs 

 gradually shrivel up and set the insects free, which 

 carry the pollen with them, so that those which then 

 visit another plant can hardly fail to deposit some of 

 it on the stigmas. Sometimes more than a hundred 

 small flies will be found in a single Arum. In these 

 two cases there is obviously a great advantage in 

 the fact that the stigmas arrive at maturity before 

 the anthers. 



Our common Scrophularia nodosa, some species of 

 Plantago, &c., are also proterogynous, but these cases 

 are comparatively rare. 



On the other hand those in which the anthers come 

 to maturity before the pistil are much more numerous. 

 To the category of these plants, which are cz\\&A prote- 

 randrous, belong some species of Thyme, Pinks, Epilo- 

 bium (Figs. 47, 48), Geranium (Fig. 40), Malva (Figs. 

 43, 44), (Mallow), Impatiens, Gentians, many of the 

 Labiatae, the Umbellifers, most of the Composites, 

 of the Lobeliaceae, and Campanulaceae. In fact, the 

 greater number of flowers which contain both stamen.'* 

 and pistil, are more or less proterandrous. 



