DEVELOPMENT OF PLANTS 



461 



secondary receptacle, bearing compartments like the normal fruit, 

 is introduced. This never reaches very large dimensions and 

 may readily be seen at one end of the orange. The original 

 stock from which the navel oranges grown in our country have 

 been derived, was obtained from Brazil. 



The Buckthorn order, Rhamnales, is very closely allied to the 



Fig. 321. Flowers of the Gsraniales and Rhamnales: A, inflorescence 

 of Geranium. B, nearly mature fruit consisting of five united carpels. C, 

 discharge of the seed. The carpds snap apart, owing to the tension set up by 

 the drying out of the tissues. D, section of pistil, showing the ovules with 

 micropyle directed upwards. E, flower of the grape {Vitis), a common form 

 of the Rhamnales — ca, calyx, reduced to a rim; c, corolla, which opens at 

 base and falls off as a cap; n, nectar glands within stamens. Compare Sapin- 

 dales. F, corolla free from the receptacle. G, flower freed from corolla, 

 ovary in section, showing micropyle pointing down as in Sapindales. 



Sapindales and includes such familiar plants as the buckthorn 

 {Rhamnus), Jersey tea (Ceanothus) , used in revolutionary times 

 as a substitute for tea, the grape (Vitis), Japanese ivies, Virginia 

 creeper (Parthenocissus) , etc. The minute green or white flower 

 shows a further reduction in parts, the petals not only being fre- 

 quently suppressed, but the stamens are reduced to one whorl 



