(22) 



have not been able to observe any tendency to arrange into vertical 

 series, as in the periphery of the frond. Those which contain spores 

 are of a yellowish green colour, those containing antheridia are of a 

 bright yellow. Substance very tough and coriaceous, scarcely adhering 

 to paper. Colour, a fine rich olive green, not changing much in drying. 



The present is readily distinguished from all the other British species 

 by its serrated margins, and the receptacles formed of, and continuous 

 with, the divisions of the frond, from which they are not otherwise 

 distinguishable than by their colour or more thickened substance, or a 

 greater tendency to irregularity in outline, being often acute, bifid, or 

 emarginate at the apices. , 



The present species is as common on all om' shores as F. vesiculosus, 

 but affects rather deejDer water, and is not so long uncovered by the tide. 

 It occupies a narrow zone from about half-tide level to nearly low-water. 

 It presents very few varieties except in the length or breadth of its 

 fronds, which vary from half an inch to nearly two inches in breadth. 



The branching of the frond is regularly dichotomous, but occasional 

 lateral innovations are found, and not imfrequently the serratures 

 become compound. The midrib generally forks before the frond, so 

 that the apices of the frond are often quite round and entire, wliilst the 

 midrib within presents forks of nearly an inch in length. Turner also 

 mentions a variety in which the serratures are almost obsolete, and 

 Greville has recorded another in which they have elongated into lacinise. 



This species is generally preferred for the purpose of exhibiting the 

 zoospores in motion. For this purpose, fronds containing receptacles of 

 a bright yellow colour are chosen, as these alone contain antheridia. A 

 few of these receptacles placed while fresh in a dry box over-night or for 

 an hour or two, will, when taken out, be observed dotted over with a bright 

 orange very tenacious fluid ; these are the antheridia, and if placed in salt 

 water under a microscope of considerable power, will be seen to consist of 

 minute cells, from the open ends of which issue iuniimerable very 

 minxite animalcule-looking bodies of an obovate form, and which imme- 

 diately commence frisking and sporting about in the most wonderful 

 manner, with the greatest activity and velocity. 



EXPLANATION OF PLATE CXXXVIII. 



Fig. 1. — Fucus serratus, natural size. 

 2. — Apex of frond with receptacles. 

 3. — Section of receptacle. 

 4. — Section of conceptacle. 

 5. — Spores from same. 

 6. — Antheridia. 

 7. — Zoospores. All magnified. 



