166 



MORPHOLOGICAL DEVELOPMENT. 



Begonia may be instanced. In B. rigida the flowers, various 

 in their attitudes, are in their more conspicuous characters 

 radial: though there is a certain bilateralness in the calyx, 

 the five petals are symmetrically disposed all round. B. 

 Wageneriana furnishes two forms of flowers. On the same in- 

 dividual plant may be. found radial flowers like Fig. 242, and 

 others, like Fig. 243, which are merging into the bilateral. 

 More decided is the bilateralness in B. albo-coccinea, Fig. 244; 

 and still more in B. nitida, Fig. 245. While in B. heraclei- 



242 



243 



244 



245 



2,46 



folia, Fig. 246, the change reaches its extreme by the dis- 

 appearance of the lateral petals. On examining the modes of 

 growth in these several species, they will be seen to explain 

 these changes in the manner alleged. Even 



more conclusive are the nearly-allied transformations occur- 

 ring in artificially-produced varieties of the same species. 

 Gloxinia may be named in illustration. In Fig. 247 is repre- 

 sented one of the ordinary forms, which shows us bilateralness 

 of shape along with a mode of growth that renders the condi- 

 tions alike on the two sides while different above and below. 

 247 24 L^ But in 0. erecta, Fig. 248, we 



have the flower assuming ai 

 upright attitude, and at the 

 same time assuming the radial 

 type. This is not to be inter- 

 preted as a production of ra- 

 dial symmetry out of bilateral symmetry, under the action of 

 the appropriate conditions. It is rather to be taken as a case 

 of what is termed " peloria " — a reversion to the primitive 

 radial type, from which the bilateral modification had been 

 derived. The significant inference to be drawn from it is, 



I 



