56 ANGIOSPERMAEDICOTYLEDONES 



sepals, which are curved inwards at the tip rather more sharply, and by the six 

 similarly shaped petals, which completely enclose the stamens so long as they are 

 not disturbed, and cover the anthers with their ends. 



The nectaries are in the form of two thick orange-coloured bodies on the base 

 of each petal, placed so close together as to touch each other. The stamens before 

 they have been stimulated lie so near the nectaries that the nectar collects in the 

 angle between the filaments and the carpels. The adhesive margin of the disk on 

 the top of the pistil functions as Sprengel recognized as a stigma. It matures 

 simultaneously with the stamens. 



When an insect in quest of nectar comes into contact with the broad 

 sensitive bases of the filaments, these suddenly move inwards towards the pistil, 

 so that the head or proboscis of the insect comes between the dehisced anthers 

 and the stigmatic margin, which is at the same level. As a rule the insect then 

 leaves the flower, and goes to another one, effecting cross-pollination in the latter 

 if it touches the stigma with that side of its body which is dusted with pollen. 

 Should insect-visits fail self-pollination automatically takes place when the flowers 

 fade, for then the anthers themselves come into contact with the stigma. Self- 

 pollination, however, does not always seem to be effective, for many flowers fail 

 to set fruits. 



According to Pfeffer, the movement of the stamens is caused by the flow of 

 water to the stimulated part. Chauveaud (' Mecanisme des mouvements provoqu^s 

 de Berberis,' C.-R. Acad, sci., Paris, cxix, 1894, pp. 103-5) describes a special 

 tissue concerned in the movement, and consisting of elongated narrow cells almost 

 fused together, with small intercellular spaces, especially at their ends. The 

 transverse walls of these cells are thin, their longitudinal ones, on the contrary, 

 are thick with numerous scattered pits. These last render possible both a very 

 rapid interchange between the cells, and also a quick bending of this elastic tissue. 

 It is covered by thin-walled cells, the contents of which constitute the active irritable 

 element. When in the resting condition, the protoplasm of each cell of the motile 

 tissue forms a thick band applied to the posterior cell-wall. On stimulation, this 

 suddenly becomes lax, spreads out, curves like a bow, and while its edges pull upon 

 the transverse walls its convex central part presses against the outer wall, which 

 becomes more strongly arched. Hence the cell becomes shorter and thicker. This 

 change in the motile tissue causes the filaments to bend inwards. 



Visitors. In accordance with the position of the nectar, these are mostly 

 insects with a medium or short proboscis. They all suck nectar, only a few bees 

 also collecting pollen. H. Miiller (H. M.) and myself (Kn.) have observed the 

 following. 



A. Coleoptera. (a) Coccinellidae : Coccinella conglobata Z. (= C. quattuor- 

 punctata Z.), skg. (H. M.); 2. C. septempunctata Z., freq., skg. (Kn.); 3. C. varia- 

 bilis Hbst., nect-lkg. (H. M.). {b) Dermestidae : 4. Attagenus pellio Z., skg. (H. M.). 

 B. Diptera. (a) Muscidae : 5. Musca corvina F., skg. (H.M.); 6. Musca domestica 

 Z., skg. (H.M., Kn.); 7. Onesia cognata Mg., ditto (H. M.) ; 8. O. floralis R.-D., 

 ditto (H. M.); 9. O. sepulcralis Mg., ditto (H. M.). (J>) Syrphtdae: 10. Ascia 

 podagrica F, freq., skg. (H. M.); 11. Eristalis arbustorum Z., skg. (H.M., Kn.); 

 12. E. nemorum Z., ditto (H. M.) ; 13. E. pertinax Scop., ditto (Kn.); 14. E. tenax 



