236 



GENERAL MORPHOLOGY OF PLANTS 



disks or root-like holdfasts. The cells contain chromatophores 

 with chlorophyll, and in addition a brown pigment (phycophczin 

 algal brown). Asexual reproduction takes place in some forms 

 by zoospores (Ectocarpus), and sexual reproduction by the union 

 of equal motile gametes. In other forms asexual reproduction 

 is wanting, but multiplication is provided for by the immense 

 number of eggs produced by a single plant (rockweed = Fucus), 

 which are fertilized by much smaller sperms. 



381. The kelps. The kelps include the largest plants found 

 among the algae. A stalk, either short or long, is present, which 

 expands into one or many leaf-like expansions, the blades, which 



are often very stout and 

 large. The stalks are 

 attached to the rocks by 

 haustoria, or grapplers, 

 which are disk-like, or 

 in many species resem- 

 ble a dense tuft of short 

 stout roots. The giant 

 kelp (Macrocystis), 

 which grows in the 

 Pacific, is 200 to 300 

 meters (700-1000 feet) 

 long. The genus Lami- 

 naria is widely distri- 

 buted and occurs on 

 both the Atlantic and 

 Pacific coasts. Some 

 of these have simple 

 strap-shaped stout 

 blades 10 meters (30 feet) or more long. The digitate laminaria 

 (L. digitata) has a broad blade which is split lengthwise into a 

 number of finger-like processes. The sea palm (Poslelsia) has a 

 stout erect cylindrical stem with numerous stout blades hanging 

 from the top. The kelps are flexible and tough and are able to 

 resist the pounding of the surf on the rocky shore. Asexual repro- 



Fig. 196. 



Portion of plant of Fucus, 

 showing conceptades in en- 

 larged ends; and below the 

 vesicles (Fucus vesiculosus). 



