8 BRiTTSH SEA-WEEDS. 



of air-vessels, which are constant to the particular genera 

 and species to which they belong, there are others which 

 are occasionally developed in an abnormal manner, to 

 meet, as it were, the exceptional requirement of some 

 plant that does not usually bear them, as, for example, 

 at the tips of the fronds of large, deep-water specimens 

 of Chorda filum. 



I have endeavoured to point out the most important 

 peculiarities in the form and structure of the frond, as it 

 is developed in our " native seaweeds," but, although 

 these afford a very fair epitome of the whole marine 

 flora, it must be borne in mind that many examples of 

 brilliant colouring, magnificent size, and exquisite de- 

 licacy, both of texture and mechanism, are to be found 

 in exotic genera, no representatives of which exist on 

 our shores. 



The fructification of Sea-weeds is closely connected 

 with, and to a certain extent dependent on, the struc- 

 ture of the frond, and the consideration of it is of the 

 highest importance in the pursuit of an accurate syste- 

 matic knowledge of the class. 



Speaking in general terms of the process of fruiting 

 among the higher Alga, Dr. Harvey writes as follows : — 

 " Spores, or sporangia, appear to be formed by certain 

 cells attracting to themselves the contents of adjacent 

 cells; and, in the compound kinds, empty cells are al- 

 most always found in the neighbourhood of the fruit- 

 cells; but, with the complication of the parts of the 

 frond, the exact mode in which spores are formed be- 

 comes more difficult of observation. At length, among 

 the highest Algae, we encounter what appear to be 

 really two sexes, one analogous to the anther, and the 

 other to the pistil of flowering plants. It would seem, 



