660 



BOTANY 



PART II 



Family 3. Rosaceae ( 24 ). Characteristic features of this family 

 are the constant presence of stipules, the absence of endosperm from 

 most of the seeds, the apocarpous fruits, and, as a rule, the numerous 

 stamens (Fig. 692). The two latter features are also found in the 

 Ranunculaceae, or generally in the Polycarpicae, but the floral members 

 are there spirally arranged while in the Rosaceae they are in whorls, 

 and the flowers are perigynous. 



In many cases the increase in number of members of the androecium and 

 gynaeceum proceeds from an intercalary zone of the hollowed floral axis, and 

 continues for a considerable period. The introduction of new members is deter- 

 mined by the spatial relations, so that differences in the numbers of members are 

 found in individuals of the same species. 



The genus Spiraea has typically pentamerous flowers with superior ovaries ; 

 many species are cultivated as ornamental shrubs (Fig. 692 E). Quillaja Saponaria 

 (Fig. 693), from Chili, is an evergreen tree with shortly -stalked, alternate, 



Fio. 692. Floral diagrams of Rosaceae. A, Sorbus domestica. B, Prunus Padus. C, Rosa 

 tomenlosa. D, Sanguisorba officinalis. E, Spiraea hypericifolia. (After EICHLER.) 



leathery leaves and terminal dichasia usually consisting of three flowers. The 

 flower has a five-toothed, nectar- secreting disc projecting above the large sepals. 

 Five of the stamens stand at the projecting angles of the disc opposite the sepals ; 

 the other five are inserted opposite the petals at the inner margin of the disc. 

 Petals narrow, white. Ovary superior. Only the middle flower of the dichasium 

 is hermaphrodite and fertile, the lateral flowers are male and have a reduced 

 gynaeceum. Fruit star-shaped, composed of partial fruits. Each carpel dehisces 

 by splitting into two valves. Seeds winged. 



The genera Pyrns, Cydonia, etc., are distinguished from the other Rosaceae by 

 their inferior ovary, which usually consists of five carpels bound together by the 



