268 IP 6 t e I s i a 



strongest in the immediate sublitoral zone the 

 tips are kept worn very short so that the plant 

 presents very little surface to the waves and 

 consequently the strain on the holdfast is 

 slight and it is not torn loose. But where the 

 wave action is less violent the tip is not nearly 

 so rapidly frayed and consecjuently attains a 

 greater length, while the strain on the hold- 

 fast remains nearly constant. The anatomical 

 means by which this equilibrium is maintained 

 is extremely simi)]e. As in all the kelps the 

 growing point is situated at the junction of 

 the stipe and lamina. From this region new 

 tissue is ])rogressively pushed farther and far- 

 ther out on the lamina by the formation of 

 still newer tissue behind. When iirst formed 

 it is tough and tenacious but with age its strength 

 gradually weakens so that the tip of the lamina 

 is able to withstand but a small strain, while 

 the basal portion is quite strong. Thus the 

 length of the plant is kept balanced with the 

 force of the waves so as to prevent its being 

 torn out by the roots as is the fate of mosi 

 other kelps. 



