424 



BOTANY 



metrical (actinomorphic), e.g. Rosa, Papaver, Oxalis, but many 

 are markedly zygomorphic, as Viola, Tropaeolum, Leguminosae. All 

 degrees of cohesion of the ovary with the floral axis are found, even 

 in the same order. Thus in the Rosales, the Crassulacese have all 

 the parts of the flower quite separate; in Pyrus, the carpels are 

 more or less completely united with the floral axis, and in Ribes 

 there is a true inferior ovary. 



Among the Choripetalae are found many types of specialization of 

 the vegetative parts. The Sarraceniales (Pitcher-plants, Sundews) 

 and the Cacti (Opuntiales) are among the most remarkable cases. 



Classification of Choripetalae 



The Choripetalse may be divided into the following orders : 



1. Centrospermae 



2. Ranales 



3. Rhoeadales 



4. Sarraceniales 



5. Rosales 



6. Geraniales 



7. Sapindales 



8. Rhamnales 



9. Malvales 



10. Parietales 



11. Opuntiales 



12. Myrtiflorae 



13. Umbelliflorae 



Order I. Centrospermae 



The Centrospermae are mostly 

 herbaceous plants, whose flowers may 

 be small and inconspicuous, e.g. 

 Amarantus, Chenopodium (Fig. 408); 

 or they may be large and showy, e.g. 

 Claytonia (Fig. 410), Dianthus, Silene 

 (Fig. 410). In the latter forms, both 

 calyx and corolla are present, and 

 the flowers are said to be " Hetero- 



chlamydeous " ; in the lower types, only one set of perianth-leaves are found, and 

 the flowers are " Homochlamydeous." The ovary is in most cases " one-celled," 

 and the seeds are borne upon a central placenta, which is developed from the 

 apex of the floral axis. The ovule is usually bent (campylotropous), and the 

 endosperm is partially replaced by perisperm. In the latter respect, as well as 

 the character of the placenta, the Centrospermse suggest the Piperales, with 

 which they may possibly be connected through the Polygonales. 



D 



FIG. 407. A, Rumex crispus. Base of 

 young shoot, showing the ochrese, o. 

 B-E, Polygonum sp. 



