THE ALGAE 



129 



It may be up to 12 ft. long and is attached by an elaborate rhizoidal system. 

 It occurs between low water and 15 fathoms. 



Laminaria hyperborea (Tangles).— This species resembles L. digit at a in 

 the shape of the thallus, but differs from it in that the stipe is not smooth 

 and it expands abruptly into the palmate frond. It is a large plant, and 



Holdfast 



Old frond 



Intercalary 



growth 



zone 



New frond 



Fig. 113. — Lominario saccharino. Two 

 mature plants. The footrule shows 

 the comparative size. 



Fig. 114. — Laminaria saccharina. 

 Mode of growth of the 

 frond. 



though not as large as the last, grows up to 10 ft. long. It occurs between 

 low-tide mark and 12 fathoms (Fig. 116). 



In all species the expanded lamina has no midrib and is borne on a basal 

 stipe, which is attached to the rock surface by a holdfast of very variable 

 form. This holdfast is made up of a number of separate branches of decreas- 

 ing thickness which adhere very tightly, forming flattened discoid masses 

 immediately in contact with the rock and attached by densely packed rhizoids. 

 The lamina grows from a meristematic zone at its base, which annually 

 forms a new frond, displacing that of the previous season, which then dies off. 



Many of the species are used as food in Asia, especially by the Chinese, 

 Japanese and Russians. In Japan about ten species are eaten, and the gathering 

 between July and October is an important industry. These kelps contain 

 considerable quantities of Iodine, which is important for the functioning 



