POWERS OF ABSORPTION, ETC. 141 



vegetables the power of absorption is restricted to 

 the root, this power in sea-weed is distributed 

 over every part of the surface, for the obvious 

 reason that it is entirely immersed in the fluid 

 from which its* nutriment is extracted. As a con- 

 sequence, therefore, if a sea-weed be partly raised 

 out of the water, the portions so deprived of their 

 source of nourishment will wither and die from 

 drought, while the portions which continue im- 

 mersed will continue to thrive, without transmit- 

 ting any moisture to the part of the plant raised 

 out of the water. 



Intimately connected with the subject of the 

 physiology of the algae is that of the artificial uses 

 to which they are adapted, the peculiar properties 

 they possess, and the purposes which in nature 

 they fulfil. 



Many of them are of no inconsiderable import- 

 ance and value to mankind. All the larger species 

 of fuci already referred to were formerly very 

 largely employed in the manufacture of kelp, an 

 impure carbonate of soda used in soap-making. 

 Chloride of sodium is found in the tissues of marine 

 vegetables, and the carbonate of soda now referred 

 to is produced by the decomposition of this chlo- 

 ride. The chloride is driven off and the carbon 

 and the sodium combine with oxygen, and the 

 chemical result is the carbonate of soda or kelp. 

 The manufacture of this substance, although now 

 in some measure superseded by the introduction 

 of foreign alkali, is still of value. It was at one 

 time extensively carried on at various places along 



