LABIATAE 245 



This forms a barrier at the mouth of the flower, and must therefore be struck against 

 and pressed back by an insect visitor. 



Female flowers occur in many species. These usually grow on separate stocks, 

 much more rarely (and in some species exceedingly so) they are associated with 

 hermaphrodite flowers on the same plant, and as a rule on the same inflorescence. 

 In the latter case either each kind of flower has a special position or both forms are 

 arranged anyhow. In many species female stocks and those with both female and 

 hermaphrodite flowers are equal, or almost equal, in number to those bearing only 

 hermaphrodite ones : in others they occur less frequently, and in still others they 

 appear only very sporadically. In all species the female flowers are smaller than the 

 larger hermaphrodite ones, but both vary considerably in size. In some species 

 there are several sizes of female flowers, corresponding exactly to those of the 

 typical hermaphrodite ones. The stigma in the smaller female flowers is usually 

 fully receptive at the beginning of anthesis, but at this stage in the larger flowers of 

 many species bearing markedly protandrous hermaphrodite ones, neither is the style 

 fully developed nor the stigma mature. This peculiarity clearly shows how female 

 flowers have been derived from protandrous hermaphrodite ones. Nectar is usually 

 secreted in large quantities in most species, and often fills the bases of the more 

 vertical flowers to a height of several millimetres. In nearly or quite horizontal ones 

 it covers the bottom of the corolla-tube, usually in the form of one or several large 

 drops. A protection against the penetration of water or the escape of nectar (in 

 horizontal flowers) is provided by hairs which line the corolla-tube and usually cover 

 the bases of the filaments as well. The nectaries of female flowers are smaller 

 than those of hermaphrodite ones in proportion to the size of the flowers themselves. 



Visitors belong to all groups of flower-visiting insects, for the flowers vary 

 greatly in size, form, and colour; the rarest are beetles, the commonest bees and 

 butterflies. Only the longest-tongued bees (especially humble-bees) and butterflies 

 can reach the nectar in flowers of many species ; the latter, however, being generally 

 unbidden guests. Many species are robbed of their nectar by perforating humble- 

 bees, as the considerable depth of the corolla-tube prevents legitimate sucking, or 

 at least renders it difiicult. 



698. Ocimum Toum. 



The nectar stored in the corolla-tube is protected by hairs on the upper 

 filaments. In the first stage of anthesis the stamens bend upwards and the style 

 downwards ; in the second this movement is reversed, so that insect visitors touch 

 either anthers or stigma only, and cross-pollination is eff'ected. 



Visitors. — Delpino only saw bees — sp. of Apis, Bombus, Anthidium, and 

 Halictus. 



699. Plectranthus L'H^rit. 



2219. P. fruticosus L'H^rit. (Hildebrand, Bot. Ztg., Leipzig, xxviii, 1870, 

 pp. 657-8.) — In the protandrous flowers of this species the style with immature 

 stigma at first lies hidden among the stamens, which are situated below the entrance 

 of a spur-like outgrowth from the base of the corolla serving as a nectar-receptacle. 

 The stamens bend downwards later on, while the stigmatic branches diverge, so that 

 these only are now exposed to contact with visitors. 



