20 SYNOPSIS OF BJKITISH SEAWEEDS. 



rested on the validity of the species, the resemblance, in 

 many respects, to a dwarfed variety of Fucus nodosus sug- 

 gesting a probability thai it was only a form of thai plant. 

 Ko doubt the connection between these plants is very strong, 



yet the difference in ramification is ><> great, and the con- 

 stancy of character observed in Fucus Mackaii in many 

 widely distant localities in which it has been abundantly 

 found, is so remarkable, that added now to distinctions 

 afforded by the position of the fruit, its characters are bet- 

 ter established. Still, its habitat is anomalous, and it may 

 be urged that the peculiar characters originate in this ha- 

 bitat. The Fuci in general are attached by scutate roots 

 to rocks and stones ; Fucus Mackaii invariably lies unat- 

 tached, resting in its place, by its own weight, on mud, 

 gravel, or among loose boulders. In such situations it 

 flourishes from year to year, and fruits abundantly. The 

 pendulous receptacles have a very pretty effect. 



15. canaliculars (The channelled Fucus); frond linear, narrow, 



channelled on one side, without midrib or ah'- vessels, dicho- 



tomous ; receptacles terminal, bipartite, Linn. Syst. Nat. v. 2. 



p. 716. (Altas, PL IV. Fig. 15.) 



Fucus excisus, Linn. Pelvetia canaliculata, Due. Fucodium 



canaliculatum, /. Ag. 

 Hah. On rocky sea-shores, between high-water mark and half- 

 tide level. Perennial. Summer and autumn. 

 This species begins to vegetate on the very edge of high- 

 water mark, often in places where it is only wet by the spray. 

 In such situations it attains a dwarfish size, seldom reach- 

 ing more than an inch or two in height, but the specimens 

 sometimes arrive at maturity and produce fruit. Between 

 this, its extreme limit, and the level of half-tide, the main 

 crop is developed, the fronds attaining a greater size with 

 the increasing depth of water ; but beyond half-tide we 

 rarely, if ever, meet with Fucus canaliculatus. It evi- 

 dently requires, by its organization, exposure to the atmo- 

 sphere for a considerable period each day. Unlike most of 

 its congeners, it rarely covers wide spaces of rock, but more 

 commonly grows in scattered tufts in places where, on the 

 recess of the tide, the water rapidly drains off. 



VI. HIMANTHALIA. 

 16. lorea (The leather-thong Himanthalia) j frond top-shaped, 



