170 CRYPTOGAMOUS OR FLOWERLESS PLANTS. [SECTION 17. 



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

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

 called Confervas before their immense diversity was 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. 564). Others, of a kind which is very common 

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

 have the chlorophyll and 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 



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 large 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 cross partition separating the newer tip from the older part below ; also, how 

 the branches arise. 



Fig. 565. Two magnified individuals of a Spirogyra, forming spores by con- 

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

 are represented. 



Fig. 566. Closterium acutum, a common Desmid, moderately magnified. It is 

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



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

 the same. 



