170 CKYPTOGAMOUS OR FLOWKKLESS 1'LANTS. [.SECTION 17. 



all the Fresh-water Algae, such as those which constitute the silky threads 

 or green slime of running streams or standing pools, aud which were all 

 called Confervas before their immense divcr.Mtv \v;is known. Some are 

 formed of a single row of cells, developed each from the end of another. 

 Others branch, the top of one cell producing more than one new one 

 (Fig. 504). Others, of a kind which is very common 

 in fresh water, simple threads made of a line of cells, 

 have the chlorophyll aud protoplasm of each cell ar- 

 ranged in spiral lines or bands. 

 They form spores in a peculiar 

 way, which gives to this family the 

 designation of conjugating Algae. 



512. At a certain time two par- 

 allel threads approach each other 

 more closely ; contiguous parts of 



y 



/ 



a cell of each thread bulge or grow out, and unite when they meet; the 

 cell-wall partitions between them are absorbed so as to open a free commu- 

 nication; the spiral band of green matter in both cells breaks up; the whole 

 of that of one cell passes over into the other; and of the united contents 

 a largo green spore is formed. Soon the old cells decay, and the spore 



FIG. 564. The growing end of a branching Conferva (Cladophora glomerata), 

 much magnified; showing how, by a kind of budding growth, a new cell is formed 

 by a crosg partition separating the newer tip from the older part below; also, how 

 the branches arise. 



Fin. 505. Two magnified individuals of a Spirogvra, forming spores by con- 

 jugation; a completed spore at base: above, successive stages of the conjugation 



are represented. 



Fio. 566. Closterimn aculnin, a cnnimon Desniid, moderately magnified. It is 

 a single firm-walled ci-11, filled with green protoplasmic matter. 



Fio. 567. More magnified view of three stages of the conjugation of a pair of 

 the same. 



