XLV] 



CHRISTOPTERIS 



217 



lines. Thus Cheiropleiiria, Platycermm, and Christopteris triciispis mark three 

 progressive steps in complexity of the subsoral system. A number of other 

 Acrostichoid Ferns belonging to Chrysodiiim, Leptochilus, and Elaphoglossiim 

 have been examined (Studies VI, p. 11). The absence in them of a diplo- 

 desmic state shows that this is not inherent in the Acrostichoid spread of 

 the sorus, while it brings into greater relief those Ferns where it is present. 

 The constituents of the sorus of C. triciispis are sporangia and paraphyses : 

 the latter are septate and branched, but they are relatively few, and are 

 barely one-third the height of the mature sporangium. The chief constituents 

 are thus the sporangia, and their crowded heads only are seen from without. 

 The various ages are intermixed, and the sporangia show no grouping that 

 suggests any primitive soral relation (Fig. 725). Again this appears as a 

 feature of advance over Platyceriiim, though the hairs are here less prominent. 



Fig. 726. Sporangia of Christopteris tricuspis. a = seen obliquely from the stomial side. 

 ^=from a reverse direction. f = a sporangium in longitudinal section. ( x 125.) 



The sporangium itself is of an ordinary Leptosporangiate type with a three- 

 rowed stalk longer than the capsule. Its segmentation is three-sided: the 

 annulus consists of about 21 cells, of which about 13 are indurated: it is 

 not definitely interrupted at the insertion of the stalk, but the stomium is 

 highly organised (Fig. 726). The spore-output is typically 64, and, as in 

 Dipteris, Cheiropleuj'ia and P/atyceriitiii, there is no perispore (Schumann, 

 I.e. p. 250; Hannig, I.e. p. 339). 



The sum of the characters thus described confirms in detail the comparison 

 of C. ti'ieiispis with Cheiropleiiria. It strongly upholds the natural relation of 

 both with Platyeerinin, notwithstanding the difference of habit. But the 

 divergent mode of life of these Ferns must be kept in mind. In Cheiropleiiria 

 we see a Dipteroid hovering between a terrestrial and an epiphytic habit: in 

 Platyeerinin the habit is definitely epiphytic: but in C tricuspis it is as 



