INTRODUCTION TO CRTPTOGAMIC BOTANY. 99 



throughout the world, and extend beyond the limits of any 

 other vegetables. Their siliceous coats render the characters by 

 which they are determined capable of perfect preservation, and 

 though the species vary greatly, still, both as regards species 

 and genera, different regions of the world produce altogether 

 different forms, together with a certain quantity of cosmopolites ; 

 and many now existent, are identical with, or at any rate, 

 extremely similar to species occurring in strata anterior to 

 comparatively recent alluvial deposits. Amongst the lower 

 Chlorosperms, there are a few forms which are peculiar to 

 particular districts, but, as research extends, the numbers of 

 these will probably be greatly diminished. The curious 

 Trypotliallus anastomosans, Hook. f. and Harv., of the 

 Antarctic regions, is identical with Kiitzing's Palmodictyon 

 viride, or, at any rate, belongs to the same genus. 



80. As, however, we approach the larger and more important 

 forms of the Algse of any of the three great groups, we find 

 some marked examples of particular distribution.* The great 

 feature of our own coasts is the extreme abundance of Lami- 

 naricB, not, indeed, of species, but of individuals ; but as we 

 get further north, especially on the western coast of America, 

 and the opposite coast of Asia, they increase immensely in 

 number and importance. On the contrary, the species of 

 Sargassum require a higher temperature, and, in consequence, 

 are unknown upon our coasts, except as wanderers. In the 

 southern hemisphere, we have a host of most important Algae, 

 belonging to the genera Lessonia, Burvillcea, &c., which are 

 altogether unknown in northern regions. Caulerpa, again, is 

 a genus but little known in European Floras, except in 

 Spain and on the northern coast of the Mediterranean. It is 

 represented, to a certain degree, by a few species of Codium, 

 but our sands produce merely a few tufts of Vaucheria with- 

 out a trace of Caulerpce, which are so remarkable in many 

 warmer cHmates for the singularity of their mode of growth, 



* In all that relates to the distribution and classification of Algise, 

 I must acknowledge my obligations to Prof. Harvey, especially in his 

 work on North American Alg^, published by the Smithsonian Insti- 

 tution. 



7* 



