124 



BOTANY 



B 



The larger Kelps and Fucaceae have a highly developed body, with a 

 leaf-bearing axis suggestive of the flowering plants. Between these 

 extremes are many intermediate types. The plants are usually 

 attached, the holdfasts, or hapteres, of the larger forms being stout 

 branched roots, which anchor them very securely (PL 2). In many 

 of the larger forms, air-vesicles are developed which act as floats, 

 and in the attached forms bring the leaves to the surface of the 

 water, where they may be exposed to the action of the light. While 

 the leaves of these Algae are structurally very different from those 

 of the vascular plants, they serve the same purpose, being true 

 assimilatory organs. 



In size, some of the Kelps rival the giants among terrestrial 

 plants. The great Bladder-kelp, Nereocystis (Fig. 98), of our own 

 Pacific coast is sometimes forty to fifty metres in length, but is 

 exceeded by the Giant-kelp (Macrocystis pyriferd), which also occurs 

 along nearly the whole Pacific coast, and in the south Atlantic, and 

 is said to attain a length of two hundred to three hundred metres. 



Distribution. The Phaeophyceae 

 are generally distributed throughout 

 the ocean, but are perhaps more abun- 

 dant in the cooler and temperate 

 waters, this being especially true of 

 the larger Kelps. The Fucaceae, on 

 the other hand, are common in the 

 warmer seas. Many species, espe- 

 cially in colder regions, grow where 

 they are exposed by the tides for 

 several hours at a time. Such forms 

 are tough and leathery in consist- 

 ence, and develop a large amount of 

 mucilaginous matter which prevents 

 rapid loss of water. 



The Pacific coast of North America 

 is especially rich in Phaeophyceae, 

 especially the Kelps, of which a 

 number of peculiar genera occur. 

 Some of these, like the curious 

 " Sea-palm " (Postelsia palmceformis) 

 (PL 2), grow attached to rocks which 

 are exposed to heavy s-irf, and we 



FIG. Q5.-A,Ectocarpusgrannlosus find in these forms an extraordinary 



(x 35) ; sp, sporangia. B, a uni- development of the holdfast. A 



locuiar sporangium, more highly small number of Phaeophyceae, of 



?%. which the best known is the Gnlf- 



culosus. (E, after BEBTHOLD.) weed (Sargassum bacciferuni), of the 



