INTRODUCTION TO CRYPTOGAMIC BOTANY. 233 



Norway to Spain, and a somewhat doubtful species occurs at 

 New Holland. Hormoseira comprehends Algas in which the 

 frond, which is at first even and filiform, is inflated, so as to 

 produce moniliform chains of vesicles, parts of which are at 

 length rough with the apertures of the conceptacles. It belongs 

 exclusively to the south. Hormoseira, like Fucus, Cystoseira, 

 and Halidrys, with which the English botanist is familiar, and 

 many other genera, is distinguished by the circumstance that 

 the bladders are formed by some swollen portion of the frond ; 

 while in Sargassum they are distinct organs, performing no 

 other necessary function, though arising from the transforma- 

 tion of what would have been a branch or leaf had it gone 

 through its full course of development. 



223. Cystoseirce are abundant on our southern coasts, but 

 they are rare as we advance upwards. Their heathlike fruti- 

 cose or spinulose habit renders them conspicuous. Cystoseira 

 ericoides, especially, is remarkable for the prismatic colours 

 which it exhibits. " It appears," says Dr. Harvey, " clothed 

 with the richest tints of blue and green, more like those phos- 

 phorescent gleams that flash from the lower marine animals 

 than any vegetable colours. As each twig waves to and fro 

 in the water, the hues vary, and sometimes, when the light 

 falls partially on a branch, some portions seem covered with 

 sky-blue flowers, while others remain dark. All these beauti- 

 ful tints perish when the plant is removed from the water." 

 We know little in this country of the other section of Fuca- 

 cece, which includes those which have organs distinct from the 

 frond. A few specimens only of Sargassur)i are occasionally 

 drifted to us by the waves. Some of the genera belong ex- 

 clusively to the southern hemisphere, and Sargassum, which 

 contains a multitude of species, is a lover in general of warm 

 seas. 



224. It was stated under Rhodosperms, that the effect of a 

 stream of fresh water upon Chondrus crispus is to thicken 

 the frond, and to make it less branched. Precisely the con- 

 trary effect obtains in Fucus vesiculosus, which, in proportion 

 as it is less abundantly and constantly supplied with salt 

 water, becomes thinner and more divided, till it is a complete 



