440 



THE ROSALES 



woody forms that are valuable for lumber, resins and dyes, 

 as the red sandalwood, licorice root, gum tragacanth, balsam of 

 tolu, indigo, etc. Related to the pea family are the curious 

 sensitive plant (Mimosa) and the acacias. One of the species of 

 the Acacia develops enormous spines that are tunnelled by ants 

 that protect the trees against leaf-destroying insects. Gum ara- 

 bic is obtained from African and Australian species of Acacia. 

 One of the most interesting features of the Rosales is the 

 variety of changes to which the receptacle and ovaries are subject 

 in the ripening of the fruit. In the majority of cases, the pistil 

 ripens as an akene or follicle (splitting along one side to free 



Fig. 317. Fruits of the pea family: A, fruit or pod of the ground nut, 

 showing the manner of seed dissemination by the snapping back of the valves 

 with a twisting motion. B, fruit or lomentum of tick-trefoil (Meibomia) , 

 The lomentum breaks into as many nut-like parts as there are seeds in the 

 fruit. C, hooked bristles on the surface of lomentum. 



the seeds) or as a pod, without any considerable modification in 

 the form of the ovary. In many instances, however, this growth 

 is attended with pronounced alterations of the parts as in the 

 currants and gooseberries where the receptacle adheres to or 

 forms the ovary and the entire structure becomes succulent, form- 

 ing a berry. The same organs in the witch-hazel develop into 

 a horn-like capsule, the walls of which, after splitting open, 

 contract and pinch out the hard, smooth seed with great force. 

 In the raspberries, the ovaries are transformed into drupes which 



