MARINE BOTANY. 125 



Finally we may remark, that the higher sea- weeds require 

 tsalt for their growth. In the Baltic, the number of marine 

 Algee is much smaller than in the open sea, whose waves 

 wash the Scandinavian peninsula at the same latitudes. 

 But it does not follow from this, that salt can be regarded as 

 nutriment like water, carbonic acid, and air ; but that it is 

 rather an irritating medicine, which heightens the organic 

 activity of the organism, much in the same way that certain 

 salts aid digestion in the higher animals. 



Most of the Alg8e are covered with a thick slime, which 

 is of great importance to their preservation, as the water 

 can glide more evenly over them, and thus their power of 

 resisting the storms is augmented. 



The Sponges, of which fifty-six species are found on the 

 British coasts alone, belong to the problematical creatures 

 which stand on the border line between the animal and 

 vegetable kingdoms, and are attached to both in turn by 

 by naturalists. As, however, it wants both sensation and 

 motion, we have good reasons for classing the Sponge 

 among the marine plants. 



The body of the Sponge consists of numerous horny 

 fibres constantly intersecting each other, in which veiy 

 many pointed pieces of lime are imbedded, and is traversed 

 by a system of water-conducting canals, which commence 

 with small pores at the surface, and pour their contents 

 into the larger vessels. These, too, are finally discharged 

 through larger openings. According to the observations of 

 Dr. Grant, the water flows in through the smaller pores, 

 and out again through the larger canals, so long as the 

 Sponge remains alive. These constant currents supply it 

 with the necessary nourishment, and maintain the change 

 of substance, which these low creatures require as much as 

 the highest beings. All the horny parts are covered with 

 a semi-fluid viscous substance, in which the simple life of 

 the Sponge has its residence. It is this which secretes the 



