398 BENNETITTALES [CH. 



A fully developed seed-stalk bearing a complete seed cut across 

 in the middle region shows the following features : a concentric 

 vascular strand surrounded by thin-walled parenchyma and the 

 coloured hypodermal layer (fig. 524, D, ac), the whole being 

 enclosed in the tubular envelope of epidermal origin (Et) which 

 is more strongly developed than in the stalks of imperfect seeds : 

 there may be as many as 10 12 tubular cells on one radius. When 

 traced downwards towards the receptacle the tubular envelope 

 decreases in breadth, though the cells become more numerous 

 and smaller, until in the immediate neighbourhood of the 

 receptacle the tubular tissue is transformed into a compact 

 parenchyma of large cells each of which corresponds to a group 

 of tubes formed by the septation of the cells. Traced upwards 

 this thin-walled parenchyma gradually passes into thick-walled 

 tubes, and near the seed-base the tubular envelope is reduced to 

 two layers, an inner consisting of relatively small cells with sinuous 

 radial walls (the folded layer of Lignier) and an outer tubular 

 layer. Lignier describes an interesting abnormality, a bifid seed- 

 stalk enclosed in a common epidermis which he compares with 

 the occasional branching of the seed-stalks of Ginkgo biloba. 



Seeds. The seeds (figs. 525, 526), 67 x 2-53 mm., are 

 tetragonal or pentagonal in the upper half (fig. 527, 1, 2), the 

 angles being formed by thick but not very prominent wings of 

 tissue (fig. 524, C, c/); they are orthotropous and have a single 

 integument (figs. 525, 526). The tubular layer forming the outer 

 portion of a seed-stalk near the seed-base is prolonged over the 

 surface of the testa as a discontinuous covering in the form of 

 isolated or small groups of tubes, giving a striated appearance 

 to the seeds. This layer though apparently a part of the seed 

 is derived from the neighbouring interseminal scales of which it 

 is the epidermal layer ; it consists of elongated cells and scattered 

 stomata 1 . The folded layer persists only in the lower part of 

 the seed, being replaced by a layer of radially extended cells 

 (radial layer ; ar, figs. 524, C ; 525, ar ; 527, c) in the upper region of 

 the seed. In the micropylar region both the tubular and folded 

 layers undergo further change ; the external, tubular, layer forms 

 a kind of epidermis (at, figs. 524, 525), the subepidermal layer, 



1 Lignier (94) p. 57; (12). 



