ALG.E. 557 



substance; propagated by the division of parent cells into two halves, which 

 become more or less completely detached, and form new individuals. 

 Conjugation also takes place in some instances, in the same way as in the 

 Confervacese. 



The order Algae, exclusive of Characese, has been divided by Har- 

 vey as follows : 



1. Melanospermese : plants of an olive-green or olive-brown colour, and cellular 



or filamentous structure ; growing in the sea. Fructification contained in 

 definite capsules or receptacles, or in distinct sori. Seeds dark-coloured. 



2. Rhodospermeai : plants usually marine, of a rose-red, purple, or red-brown 



colour, leafy, cylindrical, or filamentous. Fructification usually double; 

 the primary contained in capsules, receptacles, or immersed in the frond ; 

 secondary, when present, minute granules forming sori, or imbedded in 

 distinct receptacles. Seeds red or red-brown. 



3. Chlorospermese : plants growing either in the sea, in fresh water, or in damp 



situations ; either filamentous, membranaceous, or shapeless ; either colour- 

 less, or (owing to the presence of an internal, granular, sporular mass) of 

 a grass green, very rarely purple or red colour. Fructification, green or 

 purple sporules, either filling the frond or collected into sporidia, rarely 

 contained in external capsules. 



4. Diatomacese : as already defined above. 



Lindley enumerates 283 genera, including about 2000 species. Exam- 

 ples Chara, Nitella; Fucus, Sargassum, Laminaria, Padina, Ectocar- 

 pus, Bryopsis; Ceramium, Delesseria, Rhodymenia, Chondrus; Con- 

 ferva, Ulva, Oscillatoria, Palmella, Protococcus ; Diatoma, Hornoeo- 

 cladia, Desmidium. 



1129. The plants of the order are widely distributed over the globe, 

 being found in salt and fresh water, in moist places, as on damp rocks 

 and stones, and the glass and pots of hothouses, and even in hot 

 springs. Sometimes they present collectively the appearance of green 

 slime. They derive nourishment chiefly from the medium in which 

 they grow ; and the root-like processes with which some of them are 

 provided, seem to be merely for the purpose of fixing them. Some of 

 the species are very gigantic, others very minute, requiring the aid of 

 the microscope for their detection. The lowest members of the order 

 approach very nearly to the lowest tribes of animals, and it is difficult 

 to draw a line of demarcation. Many species now considered vegetable, 

 such as Corallina officinalis and many Diatomacece, are figured as 

 animals by Ehrenberg. There are interesting movements connected 

 with the cells of many Algae, such as Oscillatoria and Nostoc. Some 

 of the species found in the ocean have conspicuous stems, which 

 sometimes present the appearance of zones in their interior (^[ 106). 

 Among the large -stemmed species may be noticed Durvillea utifa 

 and Lessonia fuscescens. Scytosiphon (Chorda) Filum attains in the 

 British seas a length of 30 or 40 feet, while Macrocystis pyrifera 

 in the Pacific ocean reaches the length of 500 to 1500 feet. Some 

 of the Laminarias of Britain have stalks of considerable size. Sar- 



