2l6 



DIPTEROID FERNS 



[CH. 



comparable with the simpler state of Cheiropleitria, and, on the other hand, 

 with a still more complex state seen in Platyceriiun. 



After passing into the sterile blade the venatio anaxeti is like that in the 

 Ferns last named. But more special interest is found in the fertile blade, 

 which is again diplodesmic. The rather fleshy expanse is traversed towards 



Fig. 724. Clu-istoptcris triciispis: portion of the soral region 

 of the sporophyll seen as a transparency. The heavier con- 

 tinuous lines represent the normal venation of the leaf which 

 lies nearer to the upper surface. The lighter broken lines 

 represent the receptacular system extended in a plane nearer 

 to the lower surface. ( x 5.) 



its upper surface by a reticulum of stronger strands, corresponding to those 

 of the sterile blade. But in addition there is a second system connected 

 with it, which in sections is seen to ramify in a plane below, spreading 

 immediately under the soral surface (Fig. 725). The relation of these two 



Fig. 725. Part or a transverse section of a sporophyll of Christopteris tricuspis, 

 showing the diplodesmic structure and the branched hairs associated with 

 the sporangia. ( x 16.) 



systems in plan is seen in Fig. 724. The primary network connected directly 

 with the mid-rib is represented in heavier lines. The subsoral system arises 

 from the intra-areolar twigs of this by branches which run obliquely to the 

 lower level. Sometimes such a twig branches little, and the whole falls 

 within a single areola: but frequently they branch freely, even fusing with 

 strands originating elsewhere and crossing from one areola to another. 

 Thus a continuous subsoral network, more elaborate than that of Platy- 

 cerium, is produced. It is represented in Fig. 724 by lighter and broken 



