W. H. GILBCIIT OX ABSENCE OF BTOMATA IX CERTAIN FERNS. 275 



The following are the species which have been examined : — 

 Hymenophyllum Asplenoides. 

 „ hirsutum. 



,, flabellatum. 



Trichomanes radicans. 

 „ alatum. 



„ tenerum. 



„ Membranacevm. 



Todea peUucida. 

 „ superba. 

 „ Fraseri. 

 „ Hymenophylloides. 



Leaves of all kinds are generally understood to possess a cuticle 

 which is continuous over all their parts. This encloses the several 

 layers of parenchyma and the vascular system. The cells of this 

 cuticle are usually thick-walled and colourless, taking no part in the 

 plant's economy, simply preserving a suitable hygrometric condition 

 within the substance of the leaf by preventing too rapid evaporation, 

 communication with the atmosphere being kept up by means of the 

 stomata and inter-cellular spaces ; the first of which are always situate 

 in the cuticle, being formed by a modification of some of its cells. 



Xow the first fact to be noticed in the structure of these ferns is 

 that they have no cuticle ; neither on the lamina of the frond, the 

 venation, or the stipes, and that in all three genera, the outermost 

 cells are the active ones, and no inter-cellular spaces are to be found. 



As already stated. Sach refers to the fact that in Hymenophyllum 

 the lamina of the frond is composed of a single layer of cells ; this 

 also proves to be the case in three of the species of Trichomanes 

 which have come under my notice, being tabular in form, becoming 

 longer and altered in outline over the venation, and looking in 

 section verv like a strinsr of beads. 



In Trichomaius membranac-um. however, we have a somewhat 

 more complicated structure. The cells in this species are more or 

 less cylindrical, being flattened where they join each c>ther. The 

 frond consists of from one to three layers of cells, or from two to 

 four, the number depending apparently upon the amount of vigour 

 at the time of development, the larger and more vigorous looking 

 fronds possessing the greater number. The venation in the fronds of 

 this fern is linear and radial from their base, and the thinnot part 

 (or where one or two cells only in thickiRS>. ;<s the case may bej is 



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