EXPLOSIVE FLOWERS. 



267 



The phenomenon of an upward discharge of pollen is also well exhibited in 

 the Melastomacese and in many Papilionaceae of the genera Astragalus, Indigofera, 

 Medicago, and Phaca, as also in Genista, Retama, Sarothamnus, Spartium, and 

 Ulex. We will select Spartium scoparium, a plant belonging to the Mediter- 

 ranean Flora (figured in vol. i. p. 331), as a representative of this group. Figs. 

 273 ^ and 273 ^ show the front views of a flower of Spartium scoparium, and one 



Fig. 274.— Transference of pollen to the bodies of insects by means of explosive apparatus. 



> Crucianella stylosa ; the pollen is being discharged from the flowers on to the belly of a hymenopterous insect. 2 Spartiuyn 

 scoparium ; in the lowest flower the keel is still closed and stretched out horizontally ; in the flower next above, the keel 

 is depressed and the stamens have spruug up ; the third flower is being visited by a Carpenter Bee (Xylocopa violacea), and 

 is ejecting its pollen on to the under surface of the insect's body. 



recognizes at once the large upturned standard, the two lateral petals and 

 underneath them the keel composed of a pair of contiguous petals. Near the 

 base of each keel-petal is observed a swelling and a depression (fig. 273^), 

 which correspond with portions of the structure of the two wings, so that the 

 latter pair of petals engages with the keel, and every pressure upon the wings 

 from above aflfects the keel also. A blunt tooth may also be seen near the base 

 of each of the wings (see fig. 273^). When the flower is closed the teeth are 

 hidden under the standard; in the open flower they are pressed against the 

 standard, and so keep the wings, and indirectly the keel, in a horizontal position. 



