374 



BOTANY 



PART 11 



nuclei result. In the oogonium one further division, and in the antheridium four 

 take place before the sexual cells are produced. Thus in Fuciis, in contrast to 

 Didijotn, only a very short haploid stage can be recognised. 



Economic Uses. — The dried stalks of Laminaria digit ata and L. Clotistoni are 

 used as dilating agents in surgery. Iodine is obtained from the ash (varec, kelp) 

 of various Laminariaceae and Fucaceae, and formerly soda was similarly obtained. 

 Many Laminarias are rich in mannite {e.g. Laminaria saccharina), and are used in 

 its production, and also as an article of food by the Chinese and Japanese. 



Class XI 



Rhodophyceae (Red Alg-ae) ("' "^' ^-) 



The Rhodophyceae or Florideae constitute an independent group 

 of the higher Algae, the phylogenetic origin of which is perhaps to 



Fig. 31.111. — I iiuinii US I risjitis. (i iiat. size.) 



be sought among the higher Green Algae. Tliey are almost ex- 

 clusively marine, and specially characterise the lowest algal region 

 on the coasts of all oceans. A few genera (e.g. Batrachospermum, 

 Lemanm) grow in fresh-water streams. 



The thallus of the lied Algae exhibits a great variety of forms. 

 The simplest forms are represented by branched filaments consist- 



