ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 835 



per cent., which nearly corresponds to the formula C 6 H| O 5 , and 

 therefore closely resembles Eeichardt's pararabin, but differs in this, 

 that when boiled with a diluted inorganic acid it yields sugar. 



5. Metarabin. After a second extraction with dilute hydrochloric 

 acid, the alga being saturated with dilute caustic soda, the filtered 

 solution precipitated with alcohol, and the precipitate purified, its 

 reaction indicates metarabin. 



6. Wood-gum. Obtained from the residue by the addition of 10 

 per cent, potash ley. Besides these was also obtained : — 



7. Cellulose. 



All these substances boiled in dilute inorganic acids pass into 

 sugar. 



Mazaea, a new genus of Cryptophycese.* — A fresh- water alga 

 recently discovered in Brazil, belonging to the group of the Stigo- 

 nemeae, has been described by Drs. E. Bornet and A. Grunow, under 

 the name of JUazcea rivularioides. This alga, remarkable in various 

 ways, externally resembles Jiivularia plicata Harv. ; its fronds are 

 rounded, more or less irregularly knobby, and attain to a diameter of 

 about 25 mm. ; at first solid and somewhat firm, they later become 

 hollow and soft. The colour of moistened specimens is of a sombre 

 green, inclining to olive. The trichomes, immersed in a homogeneous 

 colourless jelly, spread themselves around a central space ; they 

 increase towards the periphery, and become lost in the interior. 

 These trichomes give origin to branches, either scattered or unilateral, 

 which elevate themselves to the same height, and to heterocysts 

 either sessile on the side of the cells or borne on a pedicel of one to 

 three cells ; intercalary heterocysts were not observed. The hetero- 

 cysts are oblong in form, easily to be distinguished from the 

 ordinary cells by their size, and above all, by the nature of their 

 contents, which is more homogeneous; when old, they assume a 

 yellowish tint ; the chloriodide of zinc colours them purple. 

 When a cell forms a heterocyst or a branch, it first produces 

 a lateral enlargement, which is very early separated. This new 

 cell may at once change into a heterocyst, and then it will be 

 directly applied to the side of the cell, as are the heterocysts of 

 Capsosira and those on the large branches of Stigonema, or it may be 

 divided once or twice before the formation of the heterocyst, which 

 will be then pedicellated, or it may even form a cell from which a 

 branch may arise. The branches, like the heterocysts, are not 

 uniformly arranged along the length of the filament. At certain 

 spots they are closer and level. Some remain simple, others ramify, 

 none terminate in a hair. No distinct trace of a sheath was observed 

 around any of the younger portions of the trichomes, but at the base 

 the cells are sometimes surrounded with a somewhat thick envelope. 

 None of the specimens (not very numerous) examined showed the 

 least trace of spores or homogonia. 



Two characters of this genus are particularly interesting, its 

 rivulariaceous appearance, and its pedicellated heterocysts. This 



* Bull. Soc. Bot. France, xxviii. (1881) pp. 287-8 (1 pi.). 



