92 TENTH ANNUAL REPORT OF 



of cylindrical cells, strun^; end to end, these have originated by the 

 continual transverse division of an original cylindrical cell. Such a 

 frond will continually lengthen, but will make no lateral growth; 

 and consisting of a series of joints and interspaces, it correctly sym- 

 bolizes the stem of one of the higher plants, formed of a succession 

 of nodes and internodes. And the analogy is still further preserved 

 when such confervoid threads branch ; for the branches constantly 

 originate at the joints or nodes, just as do the leaves and branches of 

 the higher compound plants. 



We have then two tendencies exhibited among Algfe — the first, a 

 tendency to form membranous expansions, the symbols or types of 

 leaves ; the second, a tendency to form cylindrical bodies or_ stems. 

 Among the less perfect Alga3 the whole plant will consist either of 

 one of these foliations, or of a simple or branched stem. But 

 gradually both ideas or forms will be associated in the same in- 

 dividual," and exhibited in greater or less perfection. We shall find 

 stems becoming flattened at their summits into leaves, and leaves, by 

 the loss of their lateral membranes, and the acquisition of thicker 

 midribs, changing into stems ; and among the most highly organized 

 Algfe we shall find leaf-like lateral branches assuming the form, and 

 to a good degree the arrangement of the leaves of higher plants. Not 

 that we find among Algre proper leaves, like those of pha3nogamous 

 plants, constantly developing buds in their axils ; for even where 

 leaf-like bodies are most obvious (as in the genus Sargassum,) they 

 are merely Phyllodadia or expanded branches, as may readily be 

 seen by observing a Sargassum in a young state, and watching the 

 gradual changes that take place as the frond lengthens. These 

 changes will bo explamed in the systematic portion of my work. 



I shall now notice more particularly the varieties of habit observed 

 among the compound Algte; and first, 



OF THE ROOT. 



The root among the Algas is rarely much developed. Among 

 higher plants which derive their nourishment from the soil in which 

 they grow, and in Fungi which feed on the juices of organized bodies, 

 root-fibres, through which nourishment is absorbed, are essential to 

 the development of the vegetable. But the Alg.-e do not, in a general 

 way, derive nourishment from the soil on which they grow. We 

 find them growing indifferently on rocks "of various mineralogical 

 character, on floating timber, on shells, on iron or other metal, on 

 each other — in fine, on any substance which is long submerged, and 

 which affords a foothold. Into none of those substances do they emit 

 roots, nor do we find that they cause the decay, or appropriate to 

 themselves the constituents, of those substances. They are nourished 

 by the water that surrounds them and the various substances which 

 are dissolved in it. On those substances they frequently exert a 

 very remarkable power, effecting chemical changes which the chemist 

 can imitate only by the agency of the most powerful apparatus. 

 They actually sometimes reverse the order of chemical afiEinity, 

 driving out the stronger acid from the salts which they imbibe, and 



