• r >wo Annul* of the South African Museum. 



more commonly subcorneal (Fig. 37, d,f, ;/). and are characterised by 

 repeated shedding of the membrane, sporiferous filaments always 

 showing large numbers of such segments of the membrane in the 

 immediate neighbourhood of the heterocysts (Fig. 37, d,f, g). 



The spores are usually produced singly (Fig. 37, d, e, f, g), but 

 trichomes with a whole series (up to 5) of spores (Fig. 37, h) are 

 not uncommon. As the cell forming the spore increases in size its 

 membrane thickens very considerably and gradually takes on a 

 yellowish colour (Fig. 37, e, f, h). Later a very chai'acteristic second 

 envelope appears about the spore ; this takes the form of a broad 

 transparent wing-like structure, traversed by numerous radiating lines 

 (Fig. 37, g) and provided with a smooth thin edge. This outer 

 envelope is principally developed at the sides of the spore and scarcely 

 extends round the two ends, where it appears either truncate, or more 

 commonly concave at the upper, and somewhat rounded at the lower, 

 end (Fig. 37, g). It seems that, later, this second envelope shrinks 

 and then is merely recognisable as an irregular frayed edge to the 

 inner spore-membrane (Fig. 37, (/). It is probable that the outer 

 spore-envelope is of a mucilaginous nature, since it stains readily with 

 methyl blue. 



As far as I am aware, only one species of Cylindrospermum (viz. C. 

 catenaium, Ralfs), exhibiting production of spores in series, has 

 hitherto become known, and this shows numerous differences from our 

 species. The most characteristic feature of the latter, however, lies in 

 the nature of the spore-membranes. An outer envelope something 

 like that of C. alatosporum appears to occur also in C. stagnate 

 (Kuetz.), Bornet et Flahault, although of different shape ; there are, 

 moreover, other points of distinction from this species. A granulated 

 epispore, like that ultimately realised in the spores of our species 

 (Fig. 37, d), is found in C. majus, Kuetz., C. tmpicum, W. & Gr. S. 

 West, C. goetzii, Schmidle, etc., although whether it arises in the same 

 way as in C. alatosporum is not evident (cf. also Woloszyiiska, Stud, 

 iib. d. Phytoplankton d. Viktoriasees, Hedwigia, lv, 1914, p. 200, Tab. 

 VIII, fig.' 14). 



(3) SCYTONEMATACEAE. 



Genus SCYTONEMA Agardh. 



1. Scytonema rnirabile (Dillw.), Bornet, JSTostoc. lu'terocyst. d. Syst. 

 Alg. d. C. Agardh, etc., Bull. Soc. Bot. d. France, xxxvi, 1889, p. 12 ; 

 Forti, o//. cit., p. 517. (Syn. : S. figuration, Ag.) 



Sample 19. 



