30 A TEXT-BOOK OF BOTANY. 



oospore results, which, upon finding a favorable resting place, 

 begins shortly to develop into new Fucus plants. The plant 

 contains both iodine and bromine, chiefly combined with salts of 

 sodium and potassium, and was at one time used in medicine. It 

 also contains a bitter principle and a considerable amount of 

 mucilage. 



AscoPHYLLUM, a rock-wccd closely related to Fucus, is dis- 

 tinguished from this genus by the fact that the branches are desti- 

 tute of midribs and the spores occur in groups of four instead of 

 eight. The frond is thick and narrow, branching somewhat 

 dichotomously, and at intervals produces large, conspicuous floats, 

 which are broader than the frond. The plants occur from j/3 to 2 

 metres in length. The fruit is found in lateral branches in winter 

 and spring, and in June the receptacles fall off and are sometimes 

 found in immense quantities, covering the bottom of tide pools. 



Laminaria is one of the common kelps or devil's aprons which 

 inhabit principally the colder seas of high latitudes. They all 

 grow in pools at low-water mark, attached to the rocks and in 

 deep water, and some attain a very large size. The species vary 

 greatly in outline and habit according to the season and place of 

 growth — whether on an exposed or sheltered coast or partly ex- 

 posed at low tide. It consists of three parts (Fig. 14, A) : a 

 long, leaf-like expansion or blade supported by a more or less 

 cylindrical stalk or stipe, which in turn is attached to the rocks 

 by a hold-fast made up of a cluster of fibrous outgrowths. In 

 general the species may be classed in two groups, one in which 

 the frond is ribbon-like or long in proportion to the breadth and 

 not split up into segments, and the other in which the frond is 

 proportionally broader and fan-shaped and laciniate. To this 

 latter belongs the Laminaria digitata. There are some 25 species, 

 distinguished by the arrangement of root-fibres comprising the 

 hold-fast, the structure of the stipe, whether solid or hollow and 

 whether provided with distinct cavities containing mucilage, the 

 shape, especially of the basal portion of the lamina, and the char- 

 acter of the margin and the position of the fruit. The growing 

 portion of the lamina is at the base, as in the leaves of the Spermo- 

 phytes. The kelps of the Pacific Ocean are among the largest 

 sea-w^eeds known, the Giant Kelp, Macrocystis, attaining a length 



