Vol. 57.] AFFINITIES OF THE EH^TIC PLANT NAIADITA. 309 



combine the characters either of iV. lanceolata and N. r)etiolata. or 



J. ' 



of N. lanceolata and N. ohtusa : that is to say, these stems each bear 

 leaves of two kinds, the shapes of the leaves being those described 

 by the specific names and well figured in Buckmau's paper. Hence 

 I propose to retain only one specific name, and this must be lanceo- 

 lata, that of the type, which by good fortune is the most frequently 

 truly descriptive. 



The surface of the leaves shows clearl}- the outlines of the 

 epidermal cell-walls. The cells are long and rectangular, often 

 shortening towards the bases of the leaves. ISTo stomata are to be 

 seen, but in searching for these structures an arrangement of cells 

 like that shown in fig. 2 frequently 



arrests attention ; to this, however. Pig, 2. — Portion of a leaf of 

 I attach no special significance. K. lanceolata, sJiowing the 



The capsules are more or less arranr/ement of the cell-walls. 

 spherical and short-stalked. The (X-^O.) 

 more perfect specimens have a 

 wall which appears tessellated, as 

 it is composed of small quadrate 

 cells (fig. 1, p. 308). The larger 

 capsules measure about 0*75 mm. 

 in diameter. 



Sections of the capsules show 

 that the spores are still connected 



into tetrads (PL XIII, fig. 6). y\ /""^^ 



The spores may be dissolved out / ^ 



from the rock by dilute hydro- 

 chloric acid. They are then seen to be tetrahedral, with a triradiate 

 mark. There are two spore-coats : the exine, which is covered 

 with irregular bosses, and the intine, which is smooth. The outer 

 face of the tetrahedral spore is rounded, and at its junction with 

 the three pyramidal interior faces, both exine and intine are 

 extended to form a marginal rim (PI. XIII, figs. 8-10). This is 

 distinguished in the case of the exine by greater thickness and 

 coarser tuberculation than the rest of the membrane. The spores 

 measure 0*08 mm. in diameter, and are thus at least twice as large 

 as the spores of any recent species that has fallen under my 

 examination. 



The minute structure of the vegetative parts, so far as it is at 

 present preserved, may be studied in successive sections exposed 

 with the aid of a hone of Water-of-Ayr stone. This is a simple but 

 laborious process, involving a considerable expenditure of time. 

 Unfortunately, the stems are too thin to admit of the use of a 

 machine, so that sections cannot be taken at regular and measured 

 intervals. A slab is chosen that is known to contain a plant- 

 bearing layer close beneath one surface. This surface is then ground 

 until fragments of plant-tissue are seen through the thin film of rock 

 covering them. The grinding is then proceeded with very slowly. 

 If one is fortunate, there will be among the fragments one or more 

 pieces of stem, possibly with leaves attached. 



