DEVELOPMENT OF PLANTS 



449 



Owing to their ability to retain moisture (page 45) they can exist 

 in the crevices of rocks and upon dry soil, while the formation of 

 roots from a bit of stem or even a leaf, as well as their habit of 

 producing buds on short stems that afterward become detached 

 and grow into new plants, brings about a sure distribution and 

 explains their popular name, live-forever. 



(a) Some Variations of the Rose Order. — The active growth 

 of the base of the receptacle and the consequent crowding result 

 in an interesting series of departures from the simple type noted 



Fig. 311. Higher forms of the Rosales: A, flower of the saxifrage. B, 

 flower in section, showing the partial adhesion of receptacle to ovary. C. 

 inflorescence of currant (Ribes). D, section of flower, showing receptacle 

 forming the cavity for the ovules which is roofed over by the carpels, epi- 

 gynous flower. 



above that lead in very regular gradations to the highest forms 

 of the order. In the higher family of the saxifrages, for example, 

 which includes the saxifrage, false miterwort (Tiarella), heu- 

 chera, bishop's cap {Mitella), golden saxifrage {Chrysospleniiim) , 

 the receptacle generally adheres to the ovary (Fig. 311, A, B). 

 so that the flower is, in a measure, epigynous and the carpels are 

 reduced to two and partly fused. Passing to the families of the 

 hydrangeas, syringas (Philadelphus), currants (Ribes), etc., the 

 receptacle and carpels are quite fused (Fig. 311, C, D) and 



