EXTERNAL CONFIGURATION OF PLANTS. 187 



depth of Avater in Tvliich they grow must be taken 

 into account. The force of waves is confined to the 

 superficial layers of the ocean, and diminishes 

 inversely as the square of the depth. Hence, in deep 

 water the surface may be greatly agitated, while at 

 bottom scarcely any motion is perce^Dtible. Every 

 visitor to the sea-side must have remarked to what 

 an amount of tugging and straining a sea-weed is 

 subjected by the waves. The Flora of the strij) of 

 shore which lies between high and low water marks 

 presents a very different appearance from that of the 

 zone included between low- water mark and ten or 

 fifteen fathoms. The latter zone is characterised by 

 the presence of the larger Laminarke and Fuci. The 

 long tangle is not well adajDted for groAving in the 

 shallow water between tide marks. There would 

 be the greatest danger of the surf beating its broad 

 fronds into shreds. Lainhiaria, both on account of 

 its size and the weaker texture of its frond, is more 

 suited to the stiller depths beyond low- water mark. 

 The Fuci of the higher shore are smaller, stouter, 

 tougher in texture, and better fitted to live in the 

 rougher water of the beach. Beyond fifty fathoms, 

 owing to deficiency of light and heat, there is 

 little marine vegetation. The Corallines and Nulli- 

 pores alone extend much further; and in the abyssal 

 depths we still meet with Diatoms. On the shore, 

 then, we observe a gradual diminution in size of the 

 plants, not unlike what we notice in ascending a 

 mountain ; but on a mountain the temperature 

 diminishes as the ^v^ind-pressure increases, ^vliile on 

 the sea -bed as the temperature diminishes the force 

 of the waves also decreases. From the small size 

 of mosses we should hardly expect any great speci- 

 alisation in relation to wind. If, however, we com- 

 pare the urn and the scale-mosses, we cannot fail to 

 note a remarkable difference, which proves that even 

 among the mosses this element has not been with- 

 out its influence in determining their shapes. The 

 stalk, or seta, which bears the capsule in the 



