i6 



PHAEOPHYCEAE 



They show a similar diversity both in external form and internal structure, 

 the larger kinds often rivalling the higher plants in both respects while the 

 smaller ones are among the simplest of algae. 



It is plants of this family*, almost exclusively marine, which form the main 

 portion of the " sea-weeds " on our shores, especially that part growing on the 

 rocks between high and low water, and the same may be said of the sea coast 

 all over the world. " Kelp," from which iodine can be obtained, is made up 

 of a few common species of brown algae f. 



Fig. ii. Splachnidium rugosum (L.) Grev 

 Conceptacle, 80/1. w. r. s. 



Fig. 12. Splachnidium rugosum. Apical cell 

 in long, section, lOOO/l. W.T.S. 



While the majority of the genera of the Green ami Blue-green Algae 

 occurring in South Africa are more or less cosmopolitan in their distribution, 

 we find, on turning to the brown and reel forms, that the geographical range 

 is more restricted, and that, as a consequence, there are several genera which 

 do not occur in the Northern hemisphere. 



* See W. H. Harvey, Nereis australis, 1H47. 



■f All sea-weeds contain iodine in the form of iodides. Although there is only an 

 infinitesimal amount of these compounds in the water the sea-weeds are able to store 

 them in their tissue, hence the ashes of sea-weeds form one of the principal raw materials 

 for the manufacture of iodine. Its presence in any of these algae can In- easily demonstrated 

 under the microscope. Place a thin section of a Fucus or Laminaria or Ecklonia, etc. on 

 a slide in a little water, add a few starch grains, cover and allow a drop of a strong 

 solution of ferric chloride to enter from the edge of the coverglass. Iodine is liberated 

 and stains the starch grains blue. R. M. 



