CRYPTOGAMS 



337 



Tin: Bacteria included under tin- name Bacillus rndiricla ( JUtizobium 

 rinosarum) occur in the root-tubercles of Leguminosae, and, like certain 

 other Bacteria found in the soil (Azotobacter chroococcum), and in the sea, are 

 capable of utilising free nitrogen in their metabolism (p. 232). The denitrifying 

 Bacteria which occur in the soil and in the sea decompose nitrates and nitrite*, 

 and liberate free nitrogen. 



In addition to saprophytic and parasitic Bacteria, there are some which, though 

 possessing no chlorophyll, obtain their food from inorganic compounds only. 

 These are the Nitrite Bacteria (Nitrosomonas), and the Xitrate Bacteria (Nifi-- 

 lnn:ti-r , which live in tin- soil. The 

 former oxidises ammonia to nitrous acid, 

 and the latter oxidises tin- nitrous to 

 nitric acid. They both obtain their 

 carbon from carbonic acid, and thus 

 derive their food independently of any 

 organic food-supply (Fig. 259, cf. p. 217). 



The Myxobacteriaceae ( 4 ) are a very 

 peculiar family of Bacteria, our accurate 

 knowledge of which is in the first instance 

 due to THAXTKI:. They nearly all live 

 saprophytically on the dung of animals, 

 and in habit resemble the My. \omycetes 

 (cf. p. 340). In the vegetative stage they 

 appear as swarms of rod-shaped Bacteria 

 connected together by the gelatinous sub- 

 stance secreted by the cells, and exhibit 



Fiu. li'.'.i. Nitrifying laeteria. alter Wiiidgrad- 

 sky. a, Nitrotomonuewropeta, from Zurich ; 



li, Xili-osoiiniiiiix jin-intfiixi?, IVoni .Java ; <, 

 Xitriibt'fti r, from Queto. (From Kis< HI i:. 

 Varies, -iiber liacterien, x 1000.) 



FK;. - J00. A, Myxueoeeus iligitatuy, bright 

 ivd tVuctilicatinn occurring on dung (x 

 120). /;, I'nlycnyiuiii jrriinigenium, red 

 fructification on dog's dung (x 40). C, 

 L'hniiiii-oiiiyres fy>iVi</f i/.<, orange fructifica- 

 tion on anteloi>e'8 dung. D, young fructi- 

 fication (x 45). /-'. single cyst germinat- 

 ing (x -'00). (.1. U. after gi'KiiL : ''/:, 

 after THAXTF.R.) 



slow creeping movements. Ultimately they form fructifications that are usually 

 brightly coloured ; these have the form either of definitely limited masses of spores 

 or of cysts containing within a firm membrane the numerous spores. The cysts 

 are unstalked, or are raised singly or in groups on a stalk, formed, like the wall of 

 the cyst, of the hardened gelatinous material (Fig. 260). 



CLASS II 

 Cyanophyceae, Blue-green Algae (') 



The Cyanophyceae are simply organised unicellular or filamentous 

 Thallophytes of a bluish-green colour ; the cells or filaments are 



z 



