i.] THE VIOLET. 27 



(Ulex europceus), and the Broom (Sarothamnus scopa- 

 rius), the flower is in a state of tension, but the different 

 parts are, as it were, locked together. The action of the 

 bee, however, puts an end to this ; the flower explodes, 

 and thus dusts the bee with pollen. 



It would, however, take too long to refer to the 

 various interesting arrangements by which cross-fertili- 

 zation is secured in this great order of plants. 



It is impossible not to be struck by the marvellous 

 variety of contrivances found among flowers, and the 

 light thus thrown upon them, by the consideration 

 of their relations to insects ; but I must now call your 

 attention to certain very curious cases, in which the 

 same species has two or more kinds of flowers. Prob- 

 ably in all plants the flowers differ somewhat in size, 

 and I have already mentioned (ante, p. 13) some species 

 in which these differences have given rise to two distinct 

 classes of flowers, one large, and much visited by insects, 

 the other small, and comparatively neglected. In other 

 species, as, for instance, some of the Violets, these differ- 

 ences are carried much further. The smaller flowers 

 have no smell or honey, the corolla is rudimentary, and, 

 in fact, an ordinary observer would not recognize them 

 as flowers at all. Such " cleistogamic " flowers, as they 

 have been termed by Dr. Kuhn, are already known to 

 exist in about fifty genera. Their object probably is to 

 secure, with as little expenditure as possible, the con- 

 tinuance of the species, in cases when, from unfavourable 

 weather or other causes, insects are absent ; and under 

 such circumstances, as scent, honey, and colour are of no 

 use, it is an advantage to the plant to be spared from 

 the effort of their production. 



