HENDERSON'S HANDBOOK OF PLANTS. 



ALG 



leaves; but, though these are often strict- 

 ly symmetrical, they never follow the 

 spiral arrangement which is so marked 

 in Phcenogamia, and which exists even 

 among Mosses. In many the stem is 

 quite obliterated, and the whole plant 

 consists of an expanded membrane, con- 

 sisting of one or more strata of cells, as 

 the case may be. Frequently there is no 

 expansion, and the whole plant, whether 

 solid or fistulose, simple or branched, is 

 everywhere more or less cylindrical. In 

 other cases, again, it consists of a mere 

 string of articulations ; while in others 

 the whole is reduced to an adnate crust 

 or a shapeless jelly, or to single cells. In 

 one curious division, the frond, though 

 often much divided, consists of a single 

 cell only, however complicated, filled with 

 endochrome, (which see. ) Whatever the 

 color of Algce may be, it appears that they 

 act upon the atmosphere in the same way 

 as Phcenogamia, ; that is to say, they ab- 

 sorb carbonic acid and give out oxygen 

 under the influence of light. 



Algce, whatever may be their outward 

 form, or whatever their degree of com- 

 plication, are cellular plants, in a very 

 few instances only presenting anything 

 like vessels, though the cell-walls them- 

 selves have frequently a spiral structure. 

 The spores are often nothing more than 

 the endochromes of cells, whether termi- 

 nal or chained together like the beads of 

 a necklace, more consolidated than usual, 

 and occasionally broken up into four or 

 more distinct reproductive bodies. There 

 are often two sorts of fruit upon the same ! 

 or on different fronds, one being regular- ! 

 ly tetraspermous, (which see,) the other 

 variable in character, presenting often the 

 appearance of a capsule perforated at the 

 apex. Among the lower Algce the spores ' 



ALG 



are often furnished with one or more 

 flagelliform processes, or with vibrating 

 cilise, by means of which they move from 

 place to place for a greater or less time, 

 as if endowed with spontaneous motion, 

 till they become attached and germinate. 

 In most of the subdivisions sexual differ- 

 ences have been observed; the antheridia, 

 or male organs, containing bodies often 

 closely resembling the spermatozoa of 

 animals. In some of the species fructifi- 

 cation does not take place till the threads 

 throw out little processes, by means of 

 which a complete union with one another 

 is established, the endochrome of the 

 joint of one thread passing through their 

 lateral tube and uniting with that of an 

 opposite joint, and then forming a per- 

 fect spore. In many of the lower Algw, 

 as, indeed, in some of the higher, repro- 

 duction takes place for an indefinite 

 time by repeated subdivision ,of the orig- 

 inal individual. At times, however, the 

 proper fruit makes its appearance, and 

 sometimes in such an anomalous form as 

 to cause much perplexity. 



Algce are related, on the one hand, to 

 Funguses, and on the other to Lichens. 

 Distinctive characters are more easily de- 

 rived from their respective habits than 

 from differences of structure. The term 

 Algce had formerly a far wider range than 

 at present, and it is now almost entirely 

 confined to aquatic Cryptogamia. There 

 is no English word that will comprise the 

 whole. The most convenient, perhaps, 

 is that of Hydrophytes, which, however, 

 does not apply to the aerial species, and 

 is objectionable because there are many 

 plants with a submerged habit which are 

 not Algce. Algce are divided into three 

 great classes, each of which comprises a 

 number of very distinct groups, the more 



