158 FILICES. 



tissue are wanting, and in place of them we have the well-known T-shaped 

 trabeculae very perfectly developed traversing the lamina of the leaf and 

 enclosing the bundle-sheath. We have already observed the like arrange- 

 ment of the mechanical system in Cordaiteae, and shall meet with it again 

 further on in very many cases. In further exemplification of this subject 

 may be mentioned the figures given by Williamson l of the leaf-structure of 

 his Rhachiopteris aspera. I have satisfied myself with regard to the facts 

 in the case of both these ferns from various preparations in my possession. 

 In Pecopteris densifolia, Ren. and P. exigua 2 , there appear to be no mechanical 

 elements in the surface of the leaf, and none in Sarcopteris Bertrandi 3 . 

 Well-preserved hairs, either detached or still in situ, have been observed not 

 unfrequently in specimens from the pebbles of Grand' Croix. In one leaf- 

 fragment of a Pecopteris the substance of the under side of the leaf swells 

 up between the tertiary nerves, and forms receptacles like deep channels 

 running parallel to the course of the nerves and having the fissure which 

 forms their aperture closed by a dense growth of 'hairs ; on account of this 

 peculiarity Renault has made a separate genus of this form, which he 

 names Scaphidopteris Gilliotti, but this is hardly admissible. Lastly, 

 Renault has drawn attention to the water-stomata and epithemata over the 

 extremities of the nerves of the pinnae in a number of species ; but the 

 genus Lageniopteris which he has founded on this character is quite 

 untenable, for these organs of excretion are observed in many Pecopteridae 

 and are probably widely diffused. They are most beautifully and clearly 

 shown in the figure which Renault has given of Lageniopteris obtusiloba 4 . 

 The section has passed exactly through one of them in the longitudinal 

 direction, and we see the swollen club-shaped extremity of the tracheid- 

 portion of the vascular bundle of the leaf surrounded by a small-celled 

 epithema, in which a wide canal of exit is closed by an unusually large 

 stoma. In the other form figured the organ is traversed by the section in 

 an oblique and less favourable direction. 



Rhachiopteridae, leaf-stalks of various orders of leaf-branching, are 

 reckoned among the most numerous of petrified vegetable remains in which 

 the structure is preserved, as might be expected indeed when we consider 

 the stoutness and solidity of character which they usually possess, and the 

 wide distribution of Ferns in early periods of the earth's history. Owing to 

 their uniformity of structure they are for the most part of small importance 

 to the botanist ; still there are some forms among them which are in the 

 highest degree interesting, though unfortunately they have not yet been 

 fully explained. Their cross -section shows a homogeneous parenchyma 

 inclosing a varying number of vascular bundles of very different and often 



1 Williamson (1), vi. * Renault (2), vol. iii, 1. 19. 3 Renault (2), vol. iii, t. 19. 4 Renault 

 (2), vol. iii, t. 23, ff. 3, 4. 



