654 ALG^ OK HYDEOPHYTA. 



plants, growing on decaying organic matter, having moving zoospores, and 

 sporangia, containing round oogonia (see p. 272). 



€. Conjugatse (so called from union of cells), or Synsporeae (aiv, together) : 

 fresh-water Algae, with septate cellular tuhes contaming green matter,toften 

 arranged in spirals, reproduction by union of the contents of 2 cells (fig. 

 471, p. 266). It includes the sub-trihe Desmidieffi. 



7. Diatomaoese (Sm, through, or t^iwui, I cut, in allusion to the mode of division) : 

 inhabiting still waters and moist places ; fronds consisting of fmstula or 

 fragments, which are either angular or cylindrical, siliceous and brittle, 

 united by a gelatinous sort of substance ; propagated by the division of 

 parent cells into two halves, which become more or less completely detached, 

 and form new individuals (fig. 472, p. 267). Conjugation also takes place 

 in the same way as in the Conjugate. 



Besides these tribes, there are others specially noted by authors as 

 doubtful; among these are included Oscillatoriece : — aquatic plants with 

 moniliform filaments, which have a wavy motion, propagating by self- 

 division ; Nostochinece : — composed of moving filaments, immersed in a 

 gelatinous matter ; Palmellotceoe : — composed of more or less rounded 

 cells in a gelatinous matrix, illustrated by the plant seen in Ked-snow ; 

 Volmcinem, composed of numerous cells or zoospores, which move 

 about in water. Authors enumerate 350 genera, ' including above 

 2500 species. Examples — Fucus, Sargassum, Laminaria, Padina, 

 Ectocarpus ; Oeramium, Delesseria, Khodymenia, Chondrus ; Ulva ; 

 Vaucheria ; Saprolegnia ; Conferva, Desmidium ; Diatoma ; Oscilla- 

 toria ; Nostoc ; Palmella, Protococous ; Volvox. 



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 Gorallina officinalis and many Diatomacece, axe 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 (p. 75). 

 Among the large-stemmed species may be noticed Durinllea utilis 

 and Lessonia fuscescens. Scytosvphon (Ghorda) 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- 



