xx ii INTRODUCTION. 



which in the old frond is foxy-brown ; in the young shoots 

 pale, transparent olive. But how is it propagated ? for it 

 rarely produces fructification. It seems to me that the old 

 frond, which is exceedingly brittle, is broken by accident, 

 and the branches, continuing to live, push out young shoots 

 from all sides. Many minute pieces that I examined were 

 as vigorous as those of larger size, but they were certainly 

 not seedlings, and appeared to me to be broken branches, 

 all having a piece of old frond from which the young shoots 

 sprung. As the plant increases in size it takes something 

 of a globular figure, from the branches issuing in all direc- 

 tions, as from a centre. On our own shores we have two 

 species analogous to S. bacciferum in their mode of growth, 

 namely, Fucus Mackaii, and the variety /3. sub-ecostatus of 

 Fucus vesiculosus, (F. balticus, Ag.) Neither of these has 

 ever yet been found attached, though they often occur in 

 immense strata; the one on the muddy sea-shore, the 

 other in salt marshes ; in which situations, respectively, 

 they continue to grow and flourish. And if it be hereafter 

 shown that F. Mackaii is merely F. nodosus, altered by 

 growing under peculiar circumstances, may it not be in- 

 ferred that S. bacciferum which differs about as much 

 from S. vulgare as F. Mackaii does from F. nodosus is 

 merely a pelagic variety of that variable plant ? 



In structure, whilst there is a great variety among the 

 different tribes of Algae, we find, in material points, a per- 

 fect similarity among all. All consist of simple cellular 

 tissue, or of its elements, gelatine (or organic mucus), mem- 

 brane, and endochrome (or chlorophyll), variously elabo- 

 rated and perfected. No vessels or ducts have been 

 discovered in any, nor does woody fibre, though of com- 

 mon occurrence among the Fungi, exist in the Alga. The 

 gelatine (or mucus) is perfectly transparent in all, but differs 

 greatly in consistency in different species, but without much 



