684 



BOTANY 



PART II 



Series II. Sympetalae 



The common character of all Sympetalae is afforded by the 

 perianth which consists of a calyx and a gamopetalous corolla. The 

 flowers are, without exception, cyclic. The number of whorls -is 

 either five or four, and on this distinction the two groups Pentacyclicae 

 and Tetracydicae are based. The Sympetalae does not correspond to 

 a single closely related group but is composed of derivations of a 

 number of natural series which have attained a similar high condition 

 by progressive reduction in the number of members in the individual 

 whorls and in the number of the whorls. Thus the common character 

 of a gamopetalous corolla is purely superficial. Though the distribu- 

 tion of the various groups of Sympetalae in relation to those of the 

 Choripetalae is not adopted here, this is for reasons of space and 

 because the affinities of all the groups are not as yet certain. 



From what has been said it follows that the most natural arrange- 

 ment is according to the height of organisation, i.e. to the degree of 

 reduction that has been reached. The Pentacyclicae are therefore 

 placed first and followed by the Tetracydicae. 



A. PENTACYCLICAE 



Order 1. Erieinae 



Family 1. Ericaceae. Evergreen, shrubby plants with small, 

 often needle-shaped leaves. Anthers characterised by the possession 



FIG. 729. Arctostaphylos Uva ursi. 1, Flowering branch. 2, Flower in longitudinal section. 

 3, Pollen tetrad. , Fruit. 5, Fruit in transverse section. (After BERG and SCHMIDT.) OFFICIAL. 



of an " exothecium " (p. 545), opening by pores or splits, frequently 

 provided with horn-like appendages, on which account the group is 

 also termed Bicornes. 



