204^ 



DIPTEROID FERNS 



[CH. 



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be so similar to that in Platyzoma (Vol. II, Fig. 483), for both of these 

 features are characteristic of the Simplices. But the most striking peculiarity 

 lies in the initial structure of the leaf-trace itself, which is most nearly 

 matched by certain early fossils. The newly separated trace of CJieiropleiiria 

 passes through a Clepsydroid phase, corres- 

 ponding to that seen in Thamnopteris (Vol. II, 

 Fig, 432, 3 to 6). It is not clear what significance 

 these facts may bear: such comparisons, though 

 remarkable, should not be unduly stressed 

 phyletically. 



The vascular supply to the lateral bud arises // 



in near relation to the binary leaf-trace of its 

 adjoining leaf (Fig. 713). The nature of this 

 branching has been considered in Vol. I, pp. 

 70-78. The facts are not clearly distinctive: but 

 it is reasonable to hold that the branching 

 arose from dichotomy with unequal develop- 

 ment of the shanks, and with a close relation 

 of the leaf to the base of the arrested shank. 

 This would bring the branching of Cheh'oplcuria 

 into line with that in Matonia or Dipteris on 

 the one hand, and with Lophosoria and Metaxya 

 on the other. 



The leaf-trace undergoes further segregation 

 in its course up the petiole, and widens out in 

 the sterile blade into the venation already noted 

 (Fig. 710).! n the narrower sporophy 11 its u p ward 

 course is suggested by the sections vii, viii, in 

 Fig. 714. There are usually three main veins 

 in the fertile blade, one median and one follow- 

 ing each margin, while the expanse between is 

 served by smaller veins, and bears on the lower Fia. 714. i—vi= successive transverse 

 surface a dense mass of sporangia and para- sections of the petiole of a sterile leaf of 



, T-i • 1- • Cheiropleiiria: — i = at the base; ii=: 



physes. Ihis condition may be compared as a about 3 inches up ; iii = 4 inches; iv = 

 whole with the fertile lamina of Dipteris qtmi- 6 inches; v = 8 inches: vi = 9 inches 



^ -' irom the base, v igs. vn, vni are from 



queflircata or Lobbiana (Vol. II, Figs. 571, 572). a fertile leaf, at levels corresponding to 



If we imagine the branched sporophyll of either '"' '' "^ '^'^ ^'"'"'^^ ^''^- ^ " '"^ 

 of these species represented by a single segment and the sori spread over 

 the whole surface, the result would be the unbranched sporophyll of Cheiro- 

 pleiu'ia. There are, however, specimens in the Kew Herbarium, with two equal 

 main veins, or three apparently equal. This is in accord with the inconstancy 

 of form and main venation of the sterile blade, while it readily finds its 



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