68 



EVOLUTION OF PLANTS 



dition between these and the simplest types, like Ecto- 

 carpus (Fig. 16). Among the most characteristic of 



these larger forms 

 may be mentioned the 

 great bladder-kelps of 

 the Pacific (Macro- 

 cystis, Nereocj^stis) 

 (Fig. 17), and the 

 smaller Lamin arias of 

 the Atlantic. Many 

 of the larger kelps 

 grow where they are 

 exposed to the full 

 force of the heavy 

 surf, and this ac- 

 counts for the tough, 

 leathery consistency 

 of many of them, and 

 the powerful hold- 

 fasts or roots. 



An examination of 

 the whole class shows 

 that within it there 

 has been much such 

 an evolution of the 

 reproductive cells as 

 we have seen in sev- 

 eral groups of the 

 green algse ; but this 

 is by no means paral- 

 leled by the vegetative parts, as the largest, and, so far as 

 the plant-body is concerned, the most specialized forms, 



FIG. 17. A young plant of Nereocystis 

 Lutkeana, one of the large kelps, 

 much reduced, showing the holdfast, 

 r, and the float, v, with the large 

 leaves at its summit ; the fully grown 

 plant may reach a length of a hun- 

 dred feet or more ; B, the simple uni- 

 locular sporangia, sp, and sterile 

 hairs, or paraphyses, par, much mag- 

 nified. 



