XXXVI] CYCADEOIDEA 401 



seed and becomes several layers wide between the fibrous wings 

 in the upper part. This fleshy tissue appears to be derived from 

 the coloured, subepidermal, layer of the seed-stalk, while the 

 internal parenchyma is regarded by Lignier as the equivalent of 

 the fibrous layer of the testa. In the micropylar tube the fibrous 

 layers are replaced by 2 — 3 layers of sclerous cells (fig. 524, A, B). 

 The testa has no vascular supply: the concentric strand of the 

 seed-stalk passes through the fibrous tissue at the base of the seed 

 and reaches the base of the nucellus (fig. 525). The nucellar apex 

 extends into the lower part of the micropyle (fig. 525, n), and in 

 some cases Lignier noticed an axial canal formed by the breaking- 

 down of the cells which abutted below on a cavity above the 

 embryo, probably the remains of a pollen-chamber (figs. 525, 527). 

 No microspores have been found. Two dark spots shown at co, 

 fig. 525, may represent archegonia but this is doubtful, especially 

 as the seed contains a well-developed embryo. The nucellus is 

 free from the testa only in the apical region and a dicotyledonous 

 embryo occupies the interior without any trace of endosperm. 

 Lignier points out that in some seeds containing embryos the 

 nucellar beak is not completely perforated: in this fact and in 

 the absence of microspores in the micropylar canals he is inclined 

 to see evidence of parthenogenesis^. 



In several respects the seeds of Cycadeoidea agree with those 

 of Gnetum: reference should be made to the account of the seed 

 of Gnetum africanum in Chapter lii. and to the papers referred to 

 in the footnote^^ 



Interseminal scales. The young seed-stalks agree very closely 

 with the interseminal scales : each seed-stalk is surrounded by 

 5 — 6 scales (fig. 527) as in other Bennettitean flowers (fig. 564). 

 For the greater part of their length the interseminal scales are 

 compressed, but above the seeds, where they are free from 

 pressure (fig. 526), they become much thicker and form a covering 

 (' pericarp ') as in Cycadeoidea Gibsoniana. In its upper region an 

 interseminal scale consists of an epidermis with strongly thickened 

 inner walls, hypodermal thick-walled cells and parenchymatous 

 ground- tissue with a single axial bundle. In the lower part the 

 scale is more flattened and the thick-walled hypoderm is replaced 

 1 Lignier (11). * Berridge (11); Thoday, M. G. (11). 



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