THE ANGIOSPERMAE 



1 189 



The genus Apocvmim shows a similar but simpler arrangement. The 

 stamens are epipetalous and the anthers closely surround the stigma, which, 

 as in Asclepias, is only receptive on its under surface, so that self-pollination 



Fig. 1 162. — Asclepias curosstnica. A, Floral diagram. B, Stamen with 

 hooded appendage. C, Gynoecium with pollinia adherent to stigma. 

 D, Pair of pollinia with " translators " or retinacula, which are 

 joined by the corpusculum. {After Le Maout and Decaisne.) 



is prevented. Each anther is sterile at the base and is prolonged upwards 

 into a lignified apex, which is united to the stigma. The narrow slits 

 between the anthers are the only means of access to the nectar. The sterile 

 base of the anther secretes a viscous fluid, and when the insect visitor 

 withdraws its proboscis this fluid sticks to it and then picks up and removes 

 pollen from the upper part of the anther. Unless the insect is fairly strong, 

 it may, however, be unable to extricate itself and flies are often caught in 

 this way. 



Another remarkable modification is that shown by Salvia (Labiatae) 

 (see Fig. 1141). The stamens (two in number) are epipetalous and have 

 short filaments. The anthers are versatile and each connective is greatly 

 extended transversely into a C-form, with half an anther at each end. One 

 limb of the connective is relatively short and its anther is sterile. The other 

 limb extends upwards under the hood of the corolla and bears a fertile 

 half-anther. The sterile anther stands in the mouth of the floral tube and 

 when pushed by a proboscis it moves inwards and the upper, fertile anther is 

 brought down forciblv on to the insect's back by the bent-lever action of 

 the connective. 



A simple example, which may stand as typical of many others, is that 

 of Campanula. The base of each filament is expanded into a hood and all 

 five of these together form a covering over the nectarial surface of the ovary. 

 The only path to the nectar is down inside the tube formed by the close 

 circle of anthers, which are introse. 



