ITS VARIOUS MODIFICATIONS. 



241 



those of the primary circle, and by their alternation -with these, 

 which brings them directly opposite the petals. A third genus 

 (Rochea) exhibits the same pentamerous and normal flower as Cras- 

 sula, except that the contiguous edges of the petals slightly cohere 

 about half their length, although a little force suffices to separate 

 them : in another (Grammanthes, Fig. 362), the petals are firmly 

 united into a tube for more than half their length, and so are the 

 sepals likewise ; illustrating the fourth of the deviations above 

 enumerated (447). Next, the allied genus Cotyledon (Fig. 363) 

 exhibits in the same flower both this coalescence of similar pai-ts, 

 and an additional circle of stamens, as in Sedum. It likewise pre- 

 sents the next order of deviations, in the union (adnation) of the 

 base of its stamens to the base of the corolla, out of which they ap- 

 parently arise, as is seen in Fig. 364, 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 in- 

 deed throughout the order, with two exceptions ; one of which is 

 seen in Penthorum, where the five ovaries (Fig. 365) are united 

 below into a solid body, wliile their summits, as well as the styles, 

 are separate. The same plant also furnishes an example of the non- 

 production (or siippression) of one set of organs, that of the petals ; 

 which, aUhough said to exist in some specimens, are ordinarily want- 

 in"; alto<2;etlier. Another instance of increase in the number of parts 

 occurs in the Houseleek (Sempervivum), in which the sepals, petals, 

 and pistils vary in different species from six to twenty, and the sta- 

 mens from twelve to forty. 



450. Some illustrations of the principal diversities of the flower, 



FIG. 362. Flower of Grammanthes. 363. Flower of a Cotyledon. 364. The corolla laid 

 open, showing the two rows of stamens inserted into it. 365. The five pistils of Penthorum, 

 united. 366. A cross-section of the same. 



21 



