4 SEAWEEDS 



The first observation commonly made by a student 

 of seaweeds is of the variation of their colours. The 

 green hue that prevails throughout land vegetation, 

 except in the colours of flowers and the bark of 

 trees, is varied in the case of seaweeds with olive- 

 brown, and red forms. An artificial classification of 

 them according to their colours leads to the striking 

 result that it nearly coincides with the natural classi- 

 fication of them according to their structure and 

 development. Such an artificial classification be- 

 came firmly established, and has left its mark on the 

 names of the natural primary divisions or sub-classes 

 of Algse, viz. the Rhodophycew or Red Seaweeds ; the 

 Phceophycece, or olive-brown; the CUorophycece or 

 green; and the Cyanophyceas or blue-green. A 

 simple experiment proves that fundamentally they 

 are all green, and that the red colouring matter 

 phycoM-ythrine, the brown phycophceine, the yellowish- 

 brown phycoxanthine, and the blue pJiycocyanine are 

 each something added to the chlorophyll or leaf-green 

 that characterises vegetation in general, and by 

 virtue of which plants form the organic substances 

 necessary for their nutrition. These additional colour- 

 ing matters can be extracted by fresh water, leaving 

 the previously red, olive, &c. plants green, and they 

 differ from the green colour in this respect, since it 

 is insoluble in water. Though there occur excep- 

 tionally a few red forms, numerous blue-green, and 

 (in the diatoms only) many brown forms in fresh- 

 waters, there still remains the broad fact that these 

 colouring matters are characteristic of seaweeds, and 

 it is in the conditions of plant-life in the waters of 



