THE LASTREAS 



141 



HYMENOPHYLLUM UNILATERALE (The One-sided 

 Filmy Fern) (Plate XXXIX) 



Somewhat more common than H. Tun- 

 bridgense, and occupying precisely similar 

 habitats. The only differences, indeed, 

 are indicated in the name, as regards form 

 of frond (Fig. 145), and in the shape of 

 the spore receptacles, which in this species 

 consist also of two valves, but differ in 

 shape, as shown in Fig. 145 ; otherwise our 

 previous remarks apply exactly. 



Fig. 145 



(pinna a 



H. unilaterale 

 nd sporangium). 



THE LASTREAS (NEPHRODIUMS) (The Buckler Ferns) 



The Lastreas are also named Nephrodiums, and the latter name 

 being descriptive of the kidney-shaped spore cover of the genus, 

 we think it well to mention it, since as a distinctive name it is 

 better than a merely personal one. The latter, however, Laslrea, 

 named after a French botanist, is too familiar to dislodge from the 

 British Fernist's vocabulary, and we are the very last to attempt 

 to do so and thus contribute to the confusion already caused in 

 that connection by would-be reformers. As we have said, it is the 

 kidney-shaped indusium, or spore cover, which distinguishes this 

 genus, and this is indicated in the popular name of Buckler Ferns, 

 as distinct from the Shield Ferns, in which the cover is perfectly 

 round. This, however, is by no means the only difference, since 

 the Shield Ferns are of very different make, and are all easily 

 recognizable by the peculiar mitten-shaped pinnae, or pinnules, 

 as well as by their texture. 



There is considerable difference of opinion as to the number 

 of our native species of this genus, owing to the fact that several 

 of them run each other so close, and present so many linking or 

 intermediate forms, as to render the drawing of a hard and fast 

 line an impossibility. Several species, however, are beyond cavil, 

 viz. L. montana (oreopteris) , the Lemon-scented Fern, L. thelypteris, 

 the Marsh Fern, L. dilatata, the Broad Buckler Fern, L. rigida, the 

 Limestone Buckler Fern, and' L. cemula, the Hay-scented Fern. 

 These are accepted generally as unassailable species, though the 

 late Mr. E. J. Lowe, in his British Ferns and Where Found, put 

 forward the theory that L. czmula was merely a mountain form of 

 L. dilatata, to which it was apt to revert under unfavourable 

 conditions, an idea which we cannot possibly accept, as there are 

 marked specific differences. Another species, the commonest of all, 

 L. filix-mas, or the Male Fern, we have not ranked with the un- 

 assailables, since Mr. G. B. Wollaston discovered, and undoubtedly 

 demonstrated, that this species fell into three sub-species, each with 



