XIV. ALG^. 981 



form, have a reddish eye-spot and transparent contractile vacuole. Their mode of reproduction is not 

 satisfactorily ascertained, but young Volvoxes occupy the centre of the sphere. StepJianospheera has 

 eight biciliated green cells, placed at equal distances along the equator of a spherical cell. Gonium pre- 

 sents a flat frond of ahout sixteen cells. These organisms present two forms of cells, an active 

 and a motionless. The active cells have each a pair of vibratile cilia projecting through their hyaline 

 envelope. 



V. Cetptococcej: (including Cetptococctjs, Ulvina, and Sph^irotilus) consist of minute 

 colourless globules, floating in vinegar, aromatic vraters, &c., and are probably mycelia of 

 Mildew Fungi. — Ed.] 



The roots of Algce are sometimes absent, sometimes reduced to fulcra or claspers fixed to solid bodies, 

 as stones, shells, wood, &c. ; sometimes filamentous and descending into the sand {Caulerpa, Penicillus, 

 &c.); sometimes discoid and attached to other Alffcs like suckers (Lejolisia, Leveillea, &c.). 



The stems of Plusosporece are usually cylindric, formed of elongated cells, with thick walls, united 

 by means of a firm intercellular substance ; the stems are simple or branched, of various lengths, sometimes 

 erect, and simulating a small tree of 10 to 13 feet in height (Lessodia), sometimes swollen and bulbous at 

 the base (Ealigenia), always deprived of stomata. The stems (^stipes) of several Algce periodically lose 

 their fronds, which are annually renewed {Laminaria Cloustoni). They sometimes present distinct zones 

 on a transverse section, due to the relative size of the cells composing them : the axis is formed of large 

 cells, and called pith (stratum medullare) ; to this succeeds a median zone (stratum inter tnedium), covered 

 by an outer (stratum corticate) ; this latter is formed of rather dense cells, filled with a colouring matter, 

 •which determines the colour of the species. 



The dimensions of Algce are extremely various. Protococous measures scarcely the y^g of an inch, 

 while Macrocystis extends to nearly 1,700 feet. The frond of Haligenia hulbosa measures sometimes 13 feet 

 in width. The microscopic plant described by Montague in 1844 as Trichodesmium Ehrenhergii covered 

 the Red Sea farther than the eye could reach, over a surface of more than 200 miles, with its little 

 filaments of a brick-red colour ; hence the name ' given to the sea which this Alga sometimes colours, 

 but which several navigators have observed at different parts of the Atlantic. 



AlgcB are usually surrounded by a thicker or thinner layer of mucilage, the origin of which is very 

 obscure, and this whether they belong to the groups of microscopic unicellular Algce or to Confervce, 

 Fucacece, Floridece, &c. There are some, however, which are covered with a calcareous coat, like certain 

 CharcB ; as Anetahularia, Neomeris, CoraUina, and several other genera of the group Chlorosporem. Several 

 PKaosporecB (Laminaria, Sec), after having been washed in fresh water and dried, become covered with a 

 white efilorescence of a sweet taste (mannite). Others again appear to secrete a liquid, acid enough to 

 decompose the hardest limestone; as the singular Fuactis calcivora, observed by A. Braun on the pebbles 

 of the Lake of Neufchatel, which this little microscopic Alga (ji^ of an inch) destroys, furrowing them 

 ■with worm-like lines, often of great depth. 



Several species exhale a peculiar smell, especially some time after being taken out of the water, or 

 when moistened after having been dried ; as Polysiphonia, which smells of chlorine, Desmarestia and ' 

 Siilnphora, which exhale a sharp unwholesome smell. Certain Floridea, when moistened, smell something 

 like violets. Finally, some Oscillarice have a slight musky scent. The majority oiAlgm respire in the same 

 way as PhEcnogams ; they decompose carbonic acid in light, and disengage oxygen even when deprived 

 of gi-een matter, as M. Kosanoff' has stated. Floridece owe this remarkable property to their red pigment, 

 as De OandoUe noticed when submitting Porphyra mdgans to the action of light. The SaprolegniecB, 

 however, behave differently, as we have seen ; they absorb the oxygen of the water in which they live, and 

 respire like animals. 



Many Algce grow exclusively on others ; as IdthosipJton, Streblonema, Myriotnchia, Myrionema, 

 Machista, Erythrotriohia, Polysiphonia, &c. ; but these plants are not really parasites, they do not appear 

 to draw their sustenance from the Algts on which they grow ; the colour which certain botanists have 



' This etymology is not admissible, — Ed. 



