456 DICOTYLEDON ES. 



leaves, and ochreate stipules ; the buds are concealed in a hollow at the base 

 of the petiole. The bark falls off in large scales. $ - and ? -flowers (monoecious) 

 in crowded, spherical inflorescences which are placed at wide intervals on a 

 terminal, thin, and pendulous axis. The flowers have an insignificant calyx 

 and corolla; the < -flower has few stamens; $ -flower, perigynous, with 4 free 

 carpels, 1 pendulous, orthotropous ovule in each. Fruit a nut ; endosperm 

 absent. 5 species; frequently grown in avenues and parks. P. occidentalis 

 (N. Am.) ; P. orientalis (W. Asia.). 



Order 8. Podostemaceae. Aquatic plants, especially in swiftly running 

 water, with somewhat of an Alga-like, Moss-like, or thalloid appearance ; they 

 show themselves iu many ways to be adapted to their mode of life and situations 

 (having a dorsiventral creeping stem, the flowers sunk in hollows, a formation 

 of haptera upon the roots, and thalloid assimilating roots and thalloid stems, 

 etc.). Tropical ; 100 species. 



Family 20. Rosiflorae. 



The leaves are scattered, stipulate, or have at least a well de- 

 veloped sheath, which is generally prolonged on each side into a 

 free portion ("adnate stipules"). The flowers are regular, peri- 

 gynous or epigynous. Calyx and corolla 5 (-4)-wenm.s with the 

 usual position. The corolla is always polypetalous. The stamens 

 are present in very varying numbers (5-co) and position, but 

 always placed in 5- or 10-merous whorls ; they are frequently 20 in 

 3 whorls (10 + 5 + 5 ; see "Pigs. 494, 502, 505) ; the nearer they are 

 placed to the circumference, the longer they are ; they are gene- 

 rally incurved in the bud, or even rolled up. The number of the 

 carpels is from 1 GO ; in most cases all are individually free 

 (syncarp), and when they are united it is in every case with the 

 ovaries only, whilst the styles remain more or less free (Pomaceae, 

 species of Spiraea). The seeds have a straight embryo, and usually 

 no endosperm. 



The perianth and stamens are most frequently pcrigynous on the edge of the 

 widened receptacle; its form varies between a flat cupule and a long tube or a 

 cup (Figs. 495, 496, 498, 499, 500) ; the carpels are situated on its base or inner 

 surface, in some instances on a central conical elongation of the floral axis 

 (Fig. 496). The carpels in Pomacea also unite more or less with the hollow 

 receptacle, or this grows in and fills up the space between the carpels, so that a 

 more or less epigynous flower is formed (Fig. 504). The following numbers of 

 stamens occur: 5, 10 (in 1 whorl), 15 (10 + 5), 20 (10 + 5 + 5), 25 (10 + 10 + 5), 

 30-50 (in 10-merous whorls) compare the diagrams. The theoretical explan- 

 ation of this relation of the 10-merous whorls and their alternation with the 

 5-merous whorls is not definitely determined; a splitting of the members of the 

 5-merous whorls may be supposed, but the development shows no indication of 

 this, and it is not supported in any other way. Several genera have " gynobasic, " 

 styles, that is, the style springs from the base of the ovary (Fig. 497 A, B). 



