FERTILIZATION OE FECUNDATION. 239 



in the mud of ditches, the staminiferous plants are detached from the 

 soil, float on the surface of the water, and produce there flowers and 

 pollen ; while the pistilliferous plants send up a long peduncle (fig. 

 228), which accommodates itself to the depth of the water by being 

 spiral, and bears on its summit the flower with the pistil. By this 

 means the two organs are brought into contact, and fertilization is 

 effected. Lagarosiphon muscoides, an aquatic plant from Africa, shows 

 similar phenomena in regard to impregnation as are seen in Vallis- 

 neria. When continued wet weather comes on after the pollen has 

 been matured, and has begun to be discharged, it often happens that 

 little or no fruit is produced. In flowers where the anthers burst in 

 succession, the injury done by moisture is less likely to extend to all. 



497. In some plants the stamens, at a certain period of their develop- 

 ment, move towards the pistil, so as to scatter the contents of the anther. 

 In Parnassia palustris and Rue, they do so in succession. In Kalmia, 

 the anthers are contained in little sacs or pouches of the corolla, until 

 the pollen is mature, and when the expansion of the corolla, and the 

 elasticity of the filament, combine to liberate them, they spring towards 

 the pistil with a jerk. In Parietaria officinalis, and in the Nettle, the 

 spiral filament is kept in a folded state until the sepals expand, and 

 then it rises with elastic force and scatters the pollen. Similar pheno- 

 mena are observed in the Cornus canadensis. In the various species 

 of Barberry, the inner and lower part of the filament is irritable, and 

 when touched it causes the stamen to move towards the pistil. This 

 takes place naturally when the anther is ripe, and the recurved valves 

 covered with pollen are ready to be applied to the stigma. The species 

 of Stylidium have their anthers and stigma seated on a column, the 

 base of which is slightly swollen and irritable. When a stimulus is 

 applied, this column passes with considerable force from one side of 

 the flower to the other, rupturing the anther-lobes, and thus aiding in 

 fertilization. 



498. In certain plants the agency of insects is employed to ensure 

 fecundation. In species of Aristolochia, the tube of the calyx com- 

 pletely encloses the organs of reproduction, and the stamens are placed 

 below the stigma, so that the pollen can neither be applied directly, 

 nor be carried by the winds. These plants are said to be frequented 

 by insects, which enter the tubes and reach the little chamber at the 

 base, with the view of collecting saccharine matter. The deflexed 

 hairs in the interior of the tube prevent their escape, and in their 

 movements they apply the pollen to the stigma. When this is accom- 

 plished, the flower withers, and the insects escape. Orchidaceous 

 plants have remarkable flowers, which resemble bees, flies, spiders, 

 and in general the insects of the country in which they grow. They 

 also contain a large quantity of honey-like matter connected with the 

 essential organs, which attract insects. These insects, in searching for 



