DEVELOPMENT OF PLANTS 



205 



at different levels in the plant world and in groups in no wise 

 connected. We have noted the same state of sexuality in some 

 of the motile green algae, i. e., in Chlamydomonas and in non- 

 motile forms as Hydrodictyon and Ulothrix, and now again in 

 Ectocarpus although these plants are widely separated as far as 

 relationship is concerned and exhibit a marked variation in the 

 development of the plant body. It is also frequently to be 

 noted that plants may get along very well indeed with only a 

 sexual or an asexual method of reproduction. 



(b) The Coarser Brown Algae, the Kelps. — Under this head 

 we may consider two groups, illustrated by the kelps and rock- 

 weeds. The kelps are related to Ectocarpus and include the 

 largest and most highly organized forms of all the algae. Indeed 

 some of these forms are quite comparable in size with our shrubs 

 and trees. The Laminarias (Fig. 120, A) of our Atlantic coast 



Fig. 120. Three of the larger brown algae: A, Laminaria. B. Lessonia. 



C, Macrocystis. 



have stalked blades ten to twenty feet long. The great bladder 

 kelps of the Pacific, Nereocystis and Macrocystis, attain great 

 dimensions, the latter genus reaching a length of 500 to 900 feet 

 and Lessonia with trunk-like stems and leaf -like segments forms 

 veritable submerged forests in the Antarctic Ocean (Fig. 120, 

 B, C). These highly organized plants, however, do not show 

 any advance in sexual reproduction over the simplest form noted 

 in Ectocarpus. Much attention has been directed to the kelps 



