SECTION 17.] 



THALLOPHYTES. 



1G9 



a small orifice which in each figure is at the margin of the page. The large 

 spores are formed eight together hi a mother-cell. The miuute motile 

 filaments of the antheridia fertilize the large spores after injection into the 

 water: and then the latter promptly acquire a cell-wall and germinate. 



510. The Florideae or Rose-red series of marine Algse (which, however, 

 are sometimes greeu or brownish) are the most attractive to amateurs. 

 The delicate Porphyra or Laver is in some countries eaten as a delicacy, and 



the cartilaginous Choudrus crispus has 

 been largely used for jelly. Besides their 

 conceptacles, which contain true spores 

 (Fig. 560), they mostly have a fructifi- 

 cation in Tetraspores, that is, of spores 

 originating in fours (Fig. 559). 



511. The Grass-green Algae sometimes form broad membranous fronds, 

 such as those of the common Ulva of the sea-shore, but most of them form 



in 



WW 



MM 





rO 



wm 



563 



mere threads, either simple or branched. 



To this division belong almost 



Fig. 557. Small plant of Chondrus crispus, or Carrageen Moss, reduced in 

 size, in fruit; the spots represent the fructification, consisting of numerous tetra- 

 spores in bunches in the substance of the plant. 558. Section through the thickness 

 of one of the lobes, magnified, passing through two of the imbedded fruit-clusters. 

 559. Two of its tetraspores (spores in fours), highly magnified. 



Fig. 560. Section through a conceptacle of Delesseria Leprieurei, much magni- 

 fied, showing the spores, which are single specialized cells, two or three in a row. 



Fig. 561. A piece of the rose-red Delesseria Lepreiurei, double natural size. 

 562. A piece cut out and much magnified, showing that it is composed of a layer 

 of cells. 563. A few of the cells more highly magnified: the cells are gelatinous 

 and thick-walled. 



