388 THE SEA SHORE 



stem, and slender branches bearing hooked, leaf-like branchlets. 

 Its air-cells are small, and are arranged singly near the tips of the 

 branches ; and the spore-receptacles are cylindrical, with hooked 

 points. This weed is common on the south and west coasts, and 

 may be readily distinguished by the beautiful iridescence it displays 

 when in the water. C. fibrosa is very 

 similar in general form, but is larger, 

 and the air-vesicles are more con- 

 spicuous. It is not iridescent when in 

 the water. A third species is named 

 C. granulata from the rough and 

 knobby appearance of the stem, due to 



FIG. 274. Cystoseira numerous oval projections, from some 



ericoides of which spring the slender, much- 



divided branches. The air-vesicles are 



arranged in groups of two or three, and the spore-receptacles are 

 at the ends of the branchlets. Our last example is C. fceniculacea, 

 found on the south coast only, and readily distinguished by the 

 numerous blunt spines that cover its long branches. The air- 

 vesicles are narrow and pointed, and situated just below the fork- 

 ings of the branchlets. 



We conclude our resume of the British sea weeds with a short 

 description of the Podded Sea Oak (Halidrys siliquosa), which grows 

 in the tide pools from high-water to low-water mark, the specimens 

 inhabiting the shallow pools being only a few inches long, while those 

 that grow in deep water often reach a length of three or four feet. 

 It is an olive, shrub-like weed, with a conical, disc-like root that 

 adheres very firmly to the rock, and a pinnately-branched frond with 

 leaf-like branchlets. The air-vesicles are cylindrical and pod-like, 

 divided internally into about ten cells, and the spores are contained 

 in globular receptacles at the tips of the branchlets. 



The young algologist will probably meet with many difficulties 

 in his attempts to classify his sea weeds and name the various 

 species in his collection. In dealing with an unknown weed we 

 strongly recommend him to first determine the order to which it 

 belongs. The genus should next be settled ; and then, if possible, 

 the species. It must be remembered, however, that he who has 

 made himself acquainted with the principles of classification has 

 done good work, and that it is far better to be able to arrange the 

 weeds into properly-classified groups than to merely learn the names 

 of the different species without regard to the relations which they 



