ITS VARIOUS MODIFICATIONS. 



247 



in the related genus Tillcea, most of the species, like ours of the 

 United States, have their parts in fours, but are otherwise similar, 

 and one common European species has its parts in threes (Fig. 

 277) : that is, one or two members are left out of each circle, 

 which of course does not interfere with the symmetry of the blos- 

 som. So in the more conspicuous genus Sedum (the Stonecrop, 

 Live-for-ever, Orpine, &c.) some species are 5-merous, others 

 4-merous, and several, like our S. ternatum, have the first blossom 

 5-merous but all the rest on the same plant 4-merous. But Sedum 

 also illustrates the case of regular augmentation (447, 1st) in its 

 androecium, which consists of twice as many stamens as there are 

 members in the other parts ; that is an additional circle of stamens 

 is introduced (Fig. 285, 286), the 

 members of which may be distin- 

 guished by being shorter or a little 

 later than those of the primary circle, 

 and also more definitely by their al- 

 ternation with the primary, which 

 brings them directly opposite the pet- 

 als. A third genus (Rochea) exhibits 

 the same 5-merous and normal flower 

 as Crassula, except that the contigu- 

 ous edges of the petals slightly cohere 

 about half their length, although a 

 little force suffices to separate them : 

 in another (Grammanthes, Fig. 287), 

 the petals are firmly united into a 

 tube for more than half their length, and so are the sepals likewise ; 

 presenting, therefore, the third of the deviations above enumer- 

 ated (447). Next, the allied genus Cotyledon (Fig. 288) exhibits 

 in the same flower both this last case of the coalescence of similar 

 parts in its floral envelopes, arid an additional circle of stamens, as 

 in Sedum. It likewise presents the next order of deviations, in the 

 adnation of the base of its stamens to the base of the corolla, out 

 of which they apparently arise, as is seen in Fig. 289, where the 

 corolla is laid open and displayed. The pistils, although ordinarily 

 exhibiting a strong tendency to unite, are perfectly distinct in all 

 these cases, and indeed throughout the order, with two exceptions ; 

 one of which is seen in Penthorum, where the five ovaries (Fig. 



FIG. 285. Flower of a Sedum. 286. Cross-section of the bud. 



