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ANGIOSPERMAE—DICOTYLEDONES 



74. Lunaria L. 



Large violet homogamous flowers, devoid of odour, and with concealed nectar. 



250. L. annua L. (=L. biennis Mnch.). (Knuth, ' Bloemenbiol. Bijdragen,' 

 and Bot. Centralbl., Cassel, Ixx, 1897, pp. 339-40.) — The flower mechanism closely 

 resembles that of Matthiola incana, but the corolla-tube is only 10 mm. long, so that 

 the nectar is accessible to comparatively short-tongued insects. The calyx is deeply 

 cordate at the base, and the sepals are closely apposed, so as to hold the claws 

 of the violet petals together to form a tube. The anthers of the four long stamens 

 project half-way out of the entrance of the flower, turning their closely-juxtaposed 

 pollen-covered sides inwards. Self-pollination may, therefore, take place automatically 

 by the fall of the pollen, or may be eff'ected by insect-visits. The two short stamens 

 arch outwards at their bases, thus leaving room for the nectaries lying internal to them, 

 as well as for the secretion. The anthers of the two short stamens — like those 

 of the long ones — mature simultaneously with the stigma, and turn their dehisced 



Fig. 31. Lunaria annua, L. (from nature), (i) Flower, natural size : K, pouch at the base of the 

 calyx : a', anthers, half projecting from the entrance of the flower, (2) Stamens and pistil, after removal 

 of sepals and petals: the short stamens diverging, natural size; a', anthers of the long stamens; a-, anther 

 of one of the short stamens ; /, the lower part of the pistil visible between the filaments of the long stamens 

 which envelope it ; k, nectary with drop of nectar. (3) As (2), but X2. 



sides towards it. Self-pollination by means of the short stamens is, however, scarcely 

 possible, for the filaments of the long stamens closely surround the pistil, thus 

 protecting the stigma from contact with the anthers of the short ones. When an 

 insect visits more than one flower the pollen of these short stamens is introduced 

 between the filaments of the long ones — which are pressed apart — dusts the stigma, 

 and effects cross-pollination. 



The proboscis of an insect probing for nectar gets covered with pollen from 

 the two short stamens, for it has to be thrust between the inner sides of these 

 and the outer sides of the long stamens. Only a proboscis at least lo mm. long 

 can secure all the nectar, but one of half that length can reach that part of it which 

 ascends to the middle of the corolla-tube. 



