23i INTRODUCTION TO CEYPTOGAMIC BOTANY. 



Pygmy, Avithout bladders, and with scarcely any midrib. Such 

 is its condition when growing on salt marshes, where it is only 

 occasionally covered, in which, perhaps, it never bears fruit. 

 Fucus ceranoides is peculiarly abundant where fresh water 

 enters, but it is not confined to such localities. In proportion as 

 the salt increases, the frond becomes broader, though it still 

 remains thin in comparison with Fucus vesiculosus, of which 

 there is a variety with lateral fruit. It is destitute also of 

 bladders ; but that is a variable character, for even in large 

 forms of F. vesiculosus they are sometimes wanting. Fucus 

 nodosus, near high water, is short and bushy ; but at low water 

 it is much drawn out, and very different in habit. It has 

 been supposed that Fucus Mackaii is only a variety of this, 

 which is not attached, but flourishes amongst loose boulders, 

 gravel, and other similar matter. But the pendulous fruit 

 seems to furnish a good and certain character. Cystoseira 

 fwniculacea, again, puts on different forms, under circum- 

 stances which are perfectly appreciable. In deep water, 

 especially in summer, it has broad leaves and large bladders, 

 and is C. discors ; in shallow pools, or late in the year, it is 

 more branched, with narrower leaves, and is G. ahrotanifolia. 

 In like manner, Halidrys siliquosa is bushy and dwarfed 

 near high water, and smaller in every part than when less 

 exposed. Stilophora rhizodes, in the deep water of land- 

 locked bays, which are not liable to disturbance, acquires a 

 fistulose stem, divaricate branches, and attenuated branchlets, 

 and is then S. Lyngbyei; at least such is Dr. Harvey's opinion, 

 who remarks, moreover, that Asperoccus Turneri, when 

 growing with it, is three to four feet long, and proportionally 

 broad, whUe in shallow pools it seldom exceeds six inches. 

 Chorda filum presents strictly analogous varieties under 

 similar circumstances, as does also Dictyota dichotoma. We 

 may, therefore, safely assume that the effect of deep water on 

 Melanosperms is to enlarge the plant, and render it more 

 luxuriant, while the contrary condition is produced by shallow 

 pools. 



