324 



TRIGONOCARPALES 



[CH. 



served as a floating mechanism,, and this is intimately associated 

 with the nucellus by means of grooves engaging with short ridges 

 (fig. 497, nr) on the surface of the nucellar tissue. The exotesta 

 is divided into three valves by radial extensions of the sclerotic 

 tissue (b, c, fig. 497; at a the exotesta is shown in an unsplit 

 condition). In connexion with each radial plate are two curved 

 plates of fibrous tissue which extend towards the grooves in the 



FIG. 496. A, Pachytesta incrassata. B, Polypterocarpus anglicus. (A, after 

 Renault; B, after Kidston.) 



endotesta (fig. 497, t) : as Oliver suggests, these plates may have 

 served a mechanical purpose for the support of the bulky nucellus. 

 The peripheral region of the nucellus is supplied by several vascular 

 bundles (fig. 497, n) from the tracheal chalazal disc. The exo- 

 testa is regarded by Oliver as corresponding to the sarcotesta 

 and sclerotesta of other seeds, and the grooves in the endotesta 

 interlocking with the nucellar ridges are compared with the 



