INTRODUCTION 9 



make up for evaporation, or salt-water) should be 

 supplied drop by drop. One of the best ways of 

 cultivating seaweeds is by suspending them in 

 baskets in the sea at proper depths from anchored 

 buoys. (Sec Reinke, in Botan. Centralblatt, 1890 ; and 

 Oltmanns, in Pringsheim's Jahrbilcher, xxiii. 1891.) 



It has been commonly supposed that the composi- 

 tion of sea-water, and particularly its degree of 

 concentration, has a powerful influence on the dis- 

 tribution of seaweeds. The North Sea, where the 

 salinity reaches 3'5 per cent., is, for example, much 

 richer in its marine flora than the Baltic even the 

 western part, where the salinity is T7 per cent., and 

 still more the eastern and northern parts, where the 

 salinity declines to 0*15 per cent. Oltmanns 1 has 

 shown, however, that the degree of salinity has much 

 less influence than has been believed, but that rapid 

 variations of this condition are hostile to the exist- 

 ence of seaweeds. Where fresh water runs into the 

 sea, it arrives in conditions varying with its abun- 

 dance, with the currents it meets and forms, and 

 with the direction of winds. There are thus set 

 up differences in the density of the water, and 

 these differences, acting on the cells of seaweeds, 

 are of very detrimental effect. Oltmanns' observa- 

 tions at Warnemunde, near Rostock, are of great 

 interest in this respect. A canal there connects the 

 sea with a lake that receives almost all the fresh- 

 water of Mecklenburg, and many species of seaweeds 

 grow in this lake at places where the salinity is 

 almost nil, while almost all are absent from the canal, 

 1 Sitzungsber. d. K. preuss. Akad. d. Wiss. (Berlin. 1891.) 



