The Freshwater Algae of Africa 



579 



oblongis vel ellipticis, membrana interiore valde incrassata lutea, 

 rnembrana exteriore alaeformi pellucida striis radiantibus munita ad 

 fines subtruncata, contentu grosse grauuloso. 



Diam. cell, veget., 3 - 5-4/x ; diam. heterocyst., 5 fj. ; long, heterocyst,, 



Q a 



< — \ 



Fig. 37. — a-c. Anabaena oblonga, De Wildeman. a and h. Trie-homes with 

 spoies. c. Apex of a trichome. d—h. Cylindrospermum alatosporum.Ti.sj). 

 d. Mature spore, with heterocyst, showing the irregular remains of the 

 outer membrane of the spore, e. Trichome, with young spore. /. Ditto. 

 (j. Mature spore, with double membrane and basal heterocyst, showing 

 segments of membrane which have been shed. h. Trichome with a series 

 of young spores. All figures x 900. 



7"5-10jn; diam. spor. sine membr. ext., 9-11 /i; cum membr. ext., 

 16-21 /x; long, spor., 20-30 /x. 



Sample 6. 



This species forms a bright blue-green stratum on the mud, the 

 stratum being composed of large numbers of densely aggregated 

 trichomes, which are in part subparallel, but in other places highly 

 flexuous and intercoiled. The heterocysts are elliptical (Fig. 37, e), or 



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