THE DICOTYLEDONES 1653 



are usually five in number and each contains two to five ovules. The fruit 

 is a pseudocarp called a pome. Certain genera, e.g., Crataegus, have woody 

 carpels enclosed in the soft receptacle tissue, each carpel being called a 

 pyrene. The flowers have a pentamerous calyx and corolla and the stamens 

 number twenty or more. The plants are mostly trees or shrubs with simple 

 or pinnate stipulate leaves. 



I. Pomarieae. The only tribe. Pyrus, Mespilus, Crataegus, Cotoneaster, 

 Eriobotrya, Amelanchier. 



III. Rosoideae 



In this sub-family the carpels are either situated on a swollen receptacle 

 or enclosed within a receptacular cup. Each carpel contains one or two 

 ovules and the fruit is indehiscent and one-seeded. Occasionally there is 

 only one carpel, borne on a carpophore. The flowers are usually penta- 

 merous, though double or semi-double flowers are common, caused by the 

 transformation of the outer stamens into petals. The leaves are very 

 variable in form. The plants may be trees or shrubs but many are herbaceous. 

 It is the largest of the sub-families. 



1. Kerrieae. The stipules are distinct and the axis does not contribute 



to the formation of the fruit. The stamens are indefinite and 

 each tapers from a broad base. The carpels are few in number 

 and whorled. Kerria, Rhodotypos, Aruncus. 



2. Potentilleae. The carpels are generally numerous and are developed 



on a large rounded or convex development of the central recep- 

 tacle, which is surrounded by a distinct receptacular ring, forming 

 a saucer around the central receptacle. This tribe is usually 

 further subdivided on the structure of the fruit. 



[a) Rubinae. The fruit is an etaerio or cluster of small drupes. 



There is no epicalyx. Rubus (Fig. 15 14). 



[b) PotentiUinae. The fruit is an akene, the seed is pendulous 



and an epicalyx is present. Fragaria, PotentiUa, Sib- 

 baldia. 



[c) Dryadinae. The fruit is an akene, the seed is erect. Geum, 



Dry as. 



3. Cercucarpeae. The receptacle is more or less tubular, with a single 



carpel. The leaves are slightly stipulate. Adenostoma, Purshia. 



4. Ulmarieae. The receptacle is flat or slightly concave. The stamens 



have narrow bases to the filaments and the ten carpels ripen 

 into one-seeded, indehiscent fruits. Ulmaria. 



5. Sanguisorbeae. The persistent, urn-shaped receptacles enclose the 



carpels, which are never numerous and often are reduced 

 to two. The receptacle, together with the fruits, often 

 becomes hard and almost woody. The number of stamens is 

 very variable, but it may be reduced, even to one. Many of the 



