ii.J DIMORPHOUS PLANTS. 37 



which self-fertilisation is prevented. In the flowers 

 hitherto described, while the several species offer the 

 most diverse arrangements, we have met with no 

 differences within the limits of the same species, ex- 

 cepting those dependent upon sex. But there are 

 other species which possess flowers of two or more 

 kinds, sometimes, as in the violet, adapted to dif- 

 ferent conditions, but more frequently so constituted 

 as to ensure cross-fertilisation. In some of the violets 

 ( V. odorata, canina, &c.), besides the blue flowers with 



FIG. 36. Cleistogamous flower of FIG. 37. Section of ditto. 



Lamium ample xicaule. 



which we are all so familiar, there are other, autumnal, 

 flowers almost without petals and stamens ; which 

 indeed have scarcely the appearance of true flowers, 

 but in which numerous seeds are produced. " Cleis- 

 togamous " flowers, as these have been called, occur 

 also in Lamium amplexicaule (Figs. 36 and 37), Oxalis 

 acetosella, Trifolium subterraneum, and other plants 

 belonging to very different groups. They were, I 

 believe, first observed by Dillenius in Ruellia (" Hortus 



