ALG.E. 



453 



4. VaucheriecB. Unicellular Algae, producing two Hods of reproductive 

 organs the one resulting from the concentration of the green matter at 

 the extremity of the filaments into an oval active spore covered with cilia, 

 the other formed as a result of sexual agency. The antheridia appear in 



Fig. 513. 



Fig. 514. 



Fig. 513. Protococcus viridis, Henfr. : a, group of cells, the upper with eight in a linear 

 series, those to the left dividing; 6, zoospores set free by the solution of the 

 cell -wall; c, cell dividing into two zoospores ; d, resting- cells ; e, zoospore with 

 the cilia cast off; f, zoospore. 



Fig. 514. Palmella nivalis. 



the form of small horns placed in the proximity of ovoid sporangia. These 

 antheridia contain numerous extremely minute spermatozoids, which es- 

 caping fertilize the sporangium and determine the formation of a spore, 

 which does not germinate immediately, but only after the lapse of some 

 time (p. 442, fig. 506). 



5. Synsporece or Conjugates. Filamentous or unicellular Algae, repro- 

 duced by the process ot conj ugation. This group comprises the Desinidieae, 

 of which further notice will be found hereafter. 



6. Diatomacece. These are also alluded to in the following pages. 



Distribution, Qualities, &c. Met with universally in fresh and brackish. 

 water, some genera also on sea-coasts, growing on rocks, large Algae, &c. 

 Some of them occasionally appear suddenly in vast quantity, colouring- 

 lakes green ; or, as in the case of Palmella nivalis (fig. 514), giving rise to 

 the phenomenon called u Red Snow." Palmella cruenta (fig. 504) often 

 forms large patches of substance like half-coagulated blood on damp stones 

 and rocks. The green slimy matter of stagnant pools is mostly composed 

 of interwoven masses of filamentous Confervoids, which present most 

 beautiful and varied forms under the microscope. Ulva (marine) produces 

 large membranous fronds, which are sometimes eaten under the name 

 or Green Laver. 



OSCILLATORIACE^ (fig. 503, A). Microscopic filamentous structures, 

 usually collected into patches of definite or indefinite form, extending 

 by peripheral growth, composed of continuous tubular sheaths enclosing 

 a green or brown gelatinous matter marked by transverse striae, where the 

 substance is divided into longer or shorter pieces, often escaping from the 



