474 



LIFE-HISTOIUES 



chain somewhat larger cells are formed, each with a distinct 

 wall. Certain of these cells, called heterocysts ^ have most of 

 their protoplasm replaced by a pale or colorless cell-sap and 



Fig. 30G.— Fallen Stars {Xosloc .^pp., Fallm Slar Fannb', Xoslurfimr). 

 A-F, Nostoc paludoaum. A, chain-colony with resting e^porcs near 

 the middle and heterocysts at the ends, =''f^-. B, restinti; spores. C- 

 F, germination of resting spore, and stages in the formation of a new 

 chain-colony. G~J, Nostoc .sphfericuni. G, ffelatinoiis balls as they 

 appear in moist earth, 3 natural size. H, part of a slice cut through 

 the ball, ^<i. J, early stages in a growing colony, -V''-'. (Janczewski. 

 Thni'ct.) — Protoplasts }>luish green, cnvelnpcd in a gelatinous mass 

 which they produce. Found uiosti> in water or on nuiist earth in 

 \-arious )iarts of the world. 



})econn' iucapal)le <»r I'urlhci' dewlopinent. At ])()ints where 



the heteroc.ysts tlnis limit .^rowtli the chain eveiitually 



^ Hct'cr-o-cysl < Clr. hrlcrvs, difforenl; k!/!>(fs, a bag. 



