XLiv] PHYLLITIS 189 



structure characteristic of the genus, a feature also found in Asplenmm. Lastly, 

 the young parts are densely covered with ramenta, which bear at their apices 

 large mucilage glands similar to those of Blechnum. These characters give 

 general support to the relationship oi Phyllitis to Blechnum, while at the same 

 time the petiolar structure appears to reflect towards Asplenmm. 



The relation of the sori to the venation of the Hart's Tongue and to the 

 sinuosities of the margin is shown in Fig. 706, 30. The primary veins arising 

 from the mid-rib bifurcate twice, or sometimes more. On the outermost 

 branches of each group, and facing outwards from the centre of the branch- 

 system of each primary vein, are the elongated sori. As the sori connected 

 with the successive primary veins face one another, the consequence is the 

 arrangement typical oiPhyllitis. The slight indentations of the sinuous margin 

 correspond to these pairs of sori, and the convexities to the regions lying 

 between the forks of the primary veins : these relations in the Hart's Tongue 

 coincide with those seen in the variety Krebsii (Fig. 706, 28, a-e^. In both 

 they may be held as evidence of a suppressed pinnation still present in 

 a widening blade. Support of the correctness of this view is found in many 

 monstrous forms of the Hart's Tongue, and especially in those designated 

 laciniata. In them the position of the laciniae is very constantly inter-soral, 

 and they themselves appear to represent suppressed pinnae. 



The development of the double sorus of Phyllitis follows the same lines 

 as in the variety Krebsii. A depression of the lower surface of the young 

 sporophyll first appears, at the margins of which the indusial flaps arise as 

 upgrowths with the usual segmentation: below them right and left are 

 procambial strands (Fig. 669, 31, a). The region between them is clear of 

 vascular tissue, and its surface rises into a ridge (Fig. 669, 31, b). The indusial 

 flaps soon overlap, covering the receptacles which lie directly over the 

 vascular strands; these produce sporangia at first with indications of a 

 basipetal succession, but this soon merges into a mixed character. 



These details of similarity between Phyllitis and the Krebsii variety 

 of Blechnum punctulatiini indicate that there is here something more than 

 homoplastic likeness. They appear rather to prove a near relationship between 

 Phyllitis and Blechnum, among forms which have had in common a widening 

 of the leaf-area with suppressed pinnation : and this has led to complications 

 of the coenosoral structure. The change has worked out in arching curvatures, 

 combined with disruption; the whole being carried out in leaves which have 

 been undergoing condensation from narrow highly pinnate branching to- 

 wards a broad, and finally an entire expanse. 



Other Ferns, ranked with the common Hart's Tongue under the genus 

 Phyllitis, or closely related to it, illustrate various modifications of its simple 

 plan. For instance, P. hemiojiitis (Lag.) O. Ktze., though still retaining the 

 open venation and the sori arranged as in P. Scolopendritmi, bears auricles at 



