358 PLANTS OF NEW ZEALAND 



nourishment. But they liave :i more remarkable function 

 than this. If they are closely examined, they will be found to 

 be studded with pores, similar to the lenticels found in the 

 branches of many trees. These pores are for the purpose of 

 allowmg air to enter and leave the internal tissues of the 

 plant. The mangrove, growing in the tidal mud, where little 

 or no oxygen can get to the roots directly, turns the tips of 

 its roots into the air, and by this ingenious means obtains its 

 necessary supply of oxygen. Nor is this the only adaptation 

 of the root to its altered environment. Most rootlets are 

 provided with a small shield at the tip, technically known as 

 the " root-cap." This protects tire tender, growing point as it 

 forces its way between the particles of the soil. Such protec- 

 tion would be superfluous in plants rooting in water, — in the 

 mangrove, and in many marsh-growing plants, it is wanting. 



But the grejr-green, asparagus-like pegs which arise from 

 the thickly interlaced network of fibres, also serve another 

 purpose. One cannot but notice the similarity in their 

 appearance and arrangement, to the breakwaters formed of 

 single posts, which may be seen in many English seaports. 

 They run sometimes in straight lines, sometimes in curves, 

 and sometimes in Vandykes. Usually, they are from two to 

 four inches apart, but in some places the mud is so thickly 

 studded with them, that it would be scarcely possible to slip a 

 pencil between. When the tide is coming in, or when a flood 

 comes down the creek, these vertical pegs greatly break the 

 force of the water. They are exceedingly elastic, and spring 

 back at once into an upright position if a heavy weight is 

 placed upon them and then removed. Not content with 

 keeping back the flood, they gather in their myriad rootlets, as 

 in a sponge, all the silt and sediment that is brought down by 

 the rivers. The thick mud settles and cakes among the root 

 fibres, while the pegs hold back any sticks, straws, or rubbish 

 afloat in the water. The fibrous matting between the pe"s is 

 rarely laid bare, save after a heavy flood, and spreads widely, 



