INTRODUCTION. xli 



example, become more plentiful and more luxuriant as we 

 travel from north to south ; and, on the other hand, that 

 Ptilota plumosa, Rhodomela lycopodioides, Rhodymenia 

 sobolifera, and several others, occur more frequently and in 

 a finer state as we approach the north. Odonthalia den- 

 tata and Rhodymenia cristata are confined to the northern 

 parts of Great Britain," (the former occurs along the north 

 coast of Ireland), " while the Cystoseirae, Fucus tubercu- 

 latus, Halyseris polypodioides, Rhodymenia jubata, R. 

 Teedii, Microcladia glandulosa, Rhodomela pinastroides, 

 Laurencia tenuissima^Iridcea reniformis, and many others, 

 are confined to the southern parts." Several of these, it is 

 worth remarking, which are in England confined to the 

 coasts of Devon and Cornwall, are found in Ireland along 

 the shores of Clare and Galway, where the Land Flora, it 

 will be remembered, contains several species otherwise pe- 

 culiar to the south of Europe. Rhodymenia cristata, which 

 in Europe is not known to the south of lat. 56, and is 

 there of small size and very rare occurrence, abounds on 

 the eastern shores of America, near New York, in lat. 

 40 30', growing most luxuriantly and fruiting abundantly. 

 If we consider the distribution of the three great series 

 into which we have divided the Algae, namely, the olive, 

 the red, and the green, we shall find that the first increases 

 as we approach the tropics, where it reaches its maximum 

 of species, though perhaps not of individuals ; that the 

 second chiefly abounds in the temperate zone, being most 

 luxuriant in form and rich in species from the 55th to the 

 45th degree, and that it rapidly diminishes towards the 

 equator after it has passed the 35th ; while the third forms 

 the majority of the vegetation of the Polar seas, is parti- 

 cularly abundant (Confervete) in the colder temperate zone, 

 but its lowest forms (Ulvtc) equally distributed through all. 

 Owing to the large size and strictly social habit of our 



