The Present Position of Palaeozoic Botany. 



203 



Mr. Kiclston was thus the first to observe direct continuit}' between 

 the seed and the frond in a Fern-like Palaeozoic plant. The familj' 

 of the Neuropterideae, of which the plant in question is a represen- 

 tative, is well known from a structural point of view. As Renault 

 demonstrated in 1883, the petrified petioles named MyeloxijJon by 

 Brongniart belonged to the fronds of Neuropteris and AJdJwpteris, 

 while Weber showed (Weber 

 and S t e r z e 1 , 1896) that Mije- 

 loxijJon petioles were borne on 

 MednUosa stems. Thus we have 

 a fairly complete knowledge of 

 the anatomy in certain members 

 of the family. The stems of 

 MecluIIosa. as has long been 

 known, have a complex structure, 

 the vascular system being of the 

 '■polystelic" tj^pe, with secondary 

 formation of wood and bast 

 around each stele. This struc- 

 ture finds its simplest expression 

 in the British species MechUIosa 

 anglica (Scott, 1899), of Lower 

 Coal-Measure age (see Figs. 35 

 & 3Ô). The leaf-bases, with ty- 

 pical Myeloxijlon structure, are 

 attached to the stem. The steles 

 are three in number, each with 

 a solid axis of primaiy wood, 

 surrounded by secondary wood 

 and phloem (Fig. 36). The leaf- 

 trace bundles, given off from the Fig. B4. Neumpttris hrtrroplujUa. Seed, 

 , p r. .1 i. 1 attached to a branch of the rachis bearius: 



outer surface of the steles, are t^^ characteristic pinnules. X 2. 

 concentric in the lower part of After Kids t on. 



their course, but soon break up 



into a number of collateral strands, with external protoxjiem (Fig. 37). 

 A large number of these collateral bundles enter the petioles, which 

 thus have a very Cycadean t3"pe of structure, chiefly differing from 

 those of recent Cycads in the fact that the wood of the bundles is, 

 as a rule, wholly centripetal, while in the living family the foliar 

 bundles are mesarch. The triarch adventitious roots, which spring 

 from the stem between the leaf-bases, also bear a considerable resem- 

 blance to those of Cycads. 



The leaf of MecMlosa anglica, as shown by the characters of the 

 rachis and leaflets in the petrified specimens, was that of an Aletho- 



