The Present Position of Palaeozoic Botany. 



205 



T. olivaeforme. -was the seed of BleduUosa auglica. The petrified spe- 

 cimens of that seed are invariably associated with the rachis and 

 other organs of tlie MeduUosa. and there are certain points of structural 

 agreement which confirm the probabily of the attribution (Scott and 

 Maslen, 1906). 



The seed is a large, ovate one, 40 — 50 mm long ; quite half the 

 length, however, is occupied by the microp^-lar tube, the most remark- 

 able feature of the seed. The testa consists of two layers: the 

 outer sarcotesta, of delicate, partly lacunar tissue, bounded externally 

 by a sharply differentiated hypoderma and epidermis, and the inner, 

 ribbed, sclerotesta, consisting of dense, thick- walled tissue. The 

 nucellus appears to have been free, from the chalaza upwards, and 



M px: 



cc 



Fig. 37. MeduUosa anglica. Two collateral leaf-trace bundles in transverse section. 

 X. xylem ; px, protoxylem ; ph, phloem. X 35. 



terminates at the apex in a pollen-chamber, provided with a distinct 

 beak, as in the seed of Cordaites. The vascular system of the seed 

 was double, the outer system of bundles traversing the sarcotesta, 

 while the inner formed a complex tracheal network in the nucellus. 

 The membrane of the megaspore is evident, but the prothallus has 

 not yet been found preserved. The structure of the seed as a whole 

 presents marked analogies with that of recent Cycadean seeds, the 

 differences depending chiefly on the free nucellus, while in Cycads it 

 is adherent to the inner layer of the integument. There are also 

 considerable reseml)lances to the Palaeozoic seed Stephanospermum, of 

 which a very full account has recently been given by Prof. F.W.Oliver 

 (Oliver, 1904). An interesting feature of Stephanospernmm is the 

 remarkably perfect preservation of the pollen-grains contained in the 

 pollen-chamber of the seed; the cell-group, probably representing the 

 antheridium, is clearly shown in the pollen-grains. 



