272 



THE FLOWER. 



cases, the obliteration or diminution may be attributed to local 

 pressure or obstruction of the light, acting uniformly in all instan- 

 ces, from some constant cause. Thus the marginal or ray flowers 

 of the dense head in Composite (as in the Aster, Sunflower, Cen- 

 taurea, &c.) are not only much larger than those of the central or 

 disk flowers, which are much pressed together, but their principal 

 development is externally. It is the same in the similar head of 

 the Scabious ; where the marginal corollas are not only the larger, 

 but their exterior lobes or petals are much larger than the inner, 

 which are dwarfed, as it were, by the pressure on that side. In 

 other cases, however, we cannot give any such mechanical expla- 

 nation. In our Buckeyes (Ord. Sapindacese), for example, the 

 whole five petals are occasionally present, as they are uniformly 

 in the Horsechestnut (another species of the same genus) : but 

 more commonly a vacant space marks the place from which the 

 anterior petal has disappeared. There is also a suppression of two 

 or three stamens out of the two circles of those organs. 



483. A few diagrams will exhibit some of the stages of suppres- 

 sion, from the complete and symmetrical to the most reduced con- 



dition of the flower. 



The diagram, Fig. 337, well enough exhibits 

 the ground -pi an of 

 a 5-merous complete 

 flower, symmetrical 

 in all its parts, ex- 

 cept that 



the pistils 



are reduced from five 

 to two ; as in Sulli- 

 Fig. 338 is a diagram of a similar 

 flower, except that the petals are absent (the place they should oc- 

 cupy is denoted by the five dotted lines) : this corresponds with 

 the Elm (when pentandrous), and to Chrysosplenium, which is of 

 the same family as Sullivantia, only that there the sepals and sta- 

 mens are in fours, one being left out, perhaps we may say, 

 from each circle. Fig. 339 is a ground-plan of the flower of the 

 common Claytonia, or Spring Beauty (Ord. Portulacacese), the 



vantia (Ord. Saxifragacea?). 



FIG. 337. Ground-plan of the flower of Sullivantia, the united pistils reduced to two. 



FIG. 338. Ground-plan of a similar flower when apetalous ; the five dotted lines indicating 

 the proper position of the suppressed petals. 



FIG. 339. Ground-plan of the flower of Claytonia; the outer lines representing the calyx of 

 two sepals ; the next set the corolla of five petals ; next are the five stamens before, the. petals ; 

 and next the ovary, composed of three parts. 



