In the separation of nucellus and integument _Pachytesta_ agrees with _Stephanospermum_ and _Trigonocarpus_. There is a double series of vascular bundles in the outer part of the testa or exotesta (fig. 497, _ex_) consisting of a spongy tissue bounded externally and internally by sclerotic layers: the exotesta is succeeded by a broader endotesta of spongy consistency which Renault suggested may have 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 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 exotesta 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 interlocking of nucellus and canopy in _Lagenostoma_, as also with the ruminated endosperm of _Torreya_. [Illustration: Fig. 496. A, _Pachytesta incrassata_. B, _Polypterocarpus anglicus_. (A, after Renault; B, after Kidston.)] [Illustration: Fig. 497. _Pachytesta_. Transverse section of a seed showing the exotesta, _ex_, with sclerous layers and vascular strands (black), the endotesta (dotted), the nucellus with its ring of vascular bundles, _n_, and the prothallus, _p_. The three radial plates in the exotesta are seen at _a_, _b_, _c_, with the trabeculae, _t_, and internal to these are the grooves in the endotesta engaging with ribs on the nucellus, _nr_. (After Oliver.)]