510 ILLUSTRATIONS OF THE NATURAL ORDERS. 



simple m structure, and include the fresh-water kinds generally, as 

 well as numerous marine species ; among them those of single rows of 

 cells, or of single cells (100 - 105, 656 - 660). Some of thci^e fruc- 

 tify by conjugation (655 - 657), as is the case in those simplified 

 forms which compose the 



984. Subord. DesmidiaceBB, which are microscopic and infusory green 

 AlgiE of single cells (Fig. 100, 655), often of crystal-like forms, in- 

 vested with mucus, and belonging to fresh water. They multiply 

 largely by division, but strictly joropa^ra^e only by conjugation. Many 

 of them have long been claimed for the animal kingdom, or es- 

 teemed of ambiguous nature, on account of the free movements 

 they exhibit ; but this affords no real distinc- 

 tion. (Chap. XII., XIII.) More ambiguous 

 still, and on the lowest confines of the vegeta- 

 ble kingdom, are those minute vegetables, as 

 they doubtless are, which constitute the 



985. Subord. DiatomaccsB. These differ 

 from the last chiefly in the brown instead of 

 green color of their contents, in the siliceous 

 and durable nature of their cell-wall, and in 

 being natives of salt instead of fresh water. 

 Their movements, as they break up from 

 their connections, are still more vivid and 

 varied. Some are fixed ; others are free. 

 Some are extremely minute : others form 

 clusters of cells of considerable size. All 

 require a compound microscope for their 

 study, and a full treatise is needed to do them 

 justice. 



986. Ord. Characeee. The Chara Family 

 consists of a few aquatic plants, which have 



"^ '^^' all the simplicity of the lower Algaj in their 



vegetation, being composed of simple tubular cells placed end to 

 end, and often with a set of smaller tubes applied to the surface of 

 the main one (Fig. 1335, 1336). Hence they have been placed 

 among Alga?,. But their fructification is of a higher order. It con- 

 sists of two kinds of bodies (both shown in Fig. 1335), of which 



FIG. 1334. Branch of the common Chara, nearly the natural size. 1335 A portion magni- 

 fied, showing the lateral tubes enclosing a large central one (a portion more magnified at 1336) ; 

 also a spore, invested by a set of tubes twisted spirally around it ; and the antheridium borno 

 at its base. 



