90 



PLANTS AND MAN 



resembling higher plants, such as the gulf weed which forms 

 drifting mats of vegetation and comprises part of the Sargasso 

 Sea. Still others attain considerable size, as is the case among the 

 Kelps which are the largest thallus plants, many of them growing 

 to a length of several hundred feet and thus equalling the height 

 of many trees (fig. 58). Kelps are the only seaweeds that are 



Fig. 59. — ^The Red Algae ^re delicate in appearance and often of ornamental 



form. 



farmed much as land crops are; beds of kelp in the Pacific Ocean 

 are harvested and from them are secured the iodine and potas- 

 sium salts in which these species are particularly rich. Kelps and 

 other brown seaweeds are often used for fertilizers, and in Japan 

 they are even prized as food delicacies. 



The phylum Rhodophyta or Red Algae grow at the greatest 

 depth in the oceans, from low tide mark to the limit of light 



I 



