LABIA TAE 



712. Melissa Toum. 



275 



Protandrous or protogynous to homogamous bee flowers. Sometimes gyno- 

 dioecism or andromonoecism. 



2290. M. officinalis L. (Schulz, ' Beitrage/ II, p. 196; Knuth, Bot. 

 Centralbl., Cassel, Ixxii, 1897.) The strong odour of lemons exhaled by the foliage- 

 leaves of this species is a great attraction to cross-pollinating insects. There is no 

 nectar-guide to be found on the small, whitish flowers (at least not in those observed 

 in the garden of the Kiel Ober-Realschule at the end of August). The broad middle 

 lobe of the lower lip is closely beset with short, stiff", cylindrical hairs, which leave 

 a deep groove down the middle free for an insect's proboscis ; the spaces between 

 these hairs are thickly beset with microscopic papillae. 



The slightly arched upper lip also possesses small hairs at the entrance to the 

 corolla-tube, which, however, are longer and looser than those on the lower lip. 

 This growth of hair also extends above on to the inner surface of the corolla-tube 

 (which is 8 mm. long and curves downwards), and the way to the nectar secreted 

 and concealed at the base of the flower is therefore quite plainly indicated to the 

 proboscis of an insect. The upper part of the corolla- 

 tube widens out for a distance of about 2 mm. into an 

 opening 2^ mm. high and 2^ mm. broad, so that the 

 head of a small insect can be inserted and a proboscis 

 6 mm. long can suck all the nectar. 



The stigma usually seems to mature shortly 

 before the anthers dehisce, but many flowers are fig. 332. M^Ussa officinalis, l. 



homogamous. The anthers of the two longer (0 Flower seen directly from the front: 



_ in the entrance the anthers of the two 



Stamens dehisce before those of the two shorter shorter stamens are seen below, and 



ones. The stigma, with its two hook-shaped, w\!nhV'LVe''anSrn.ra*^etth'; 

 diverging branches, is generally situated between middle (x 3i). (2) a flower puUed 



^ '' ' out of the calyx and seen from the side. 



the anthers of the two longer stamens, sometimes 



projecting beyond them, but in other cases being somewhat shorter. It frequently 

 remains receptive until the anthers of the shorter stamens dehisce, but is often com- 

 pletely shrivelled by that time. A considerable number of flowers are entirely 

 devoid of style and stigma. I cannot say whether these varied conditions are also to 

 be found in flowers blooming earlier, having failed to examine them. 



On visiting a flower in the purely female stage, therefore, a nectar-seeking 

 insect will brush against the stigma on alighting, and dust it with pollen previously 

 gathered ; on visiting a hermaphrodite or entirely male one, it will again be dusted 

 with fresh pollen. Crossing is thus brought about by regular nectar-sucking insects ; 

 such visitors can, however, also effect self-pollination in flowers in the hermaphrodite 

 stage. This may also take place in such flowers when the stigma remains receptive 

 long enough, by contact or the falling of pollen, when the stigma is of the same 

 length as the anthers of the two longer stamens, or a little shorter. 



Schulz observed single gynodioecious stocks at Bozen, among others with 

 protandrous hermaphrodite flowers. 



Visitors. The following were recorded by the observers, and for the localities 

 stated. 



