316 T rtnuactionfi. 



brooks and springs. Streams, tco, .sometimes flow over the 

 shore. In both these cases special conditions occur for plant- 

 life, but such, it may be pointed out, are not coastal unless salt 

 be present in excess. 



3. Ecological Factors. 



The special factors with regard to coastal vegetation are 

 superabundance of salt in the soil, and high or frequent and pro- 

 longed winds. Together with these comes a more equable cli- 

 mate than further inland, so far as extremes of temperature are 

 concerned, but at the same time there is often strong insolation 

 and bright illumination. The biotic factor, apart from intro- 

 duced animals and those concerned in fertilisation, is of little 

 moment, with the exception of the part played by the small 

 land-crabs in the salt meadoM^s, whose innumerable holes must 

 assist materially in aerating the soil, and to some measure, also, 

 in draining the ground. 



As for the salt in the soil, this comes either through the flood- 

 ing of the ground more or less frequently, or through sea-spray 

 blowing inland. The effect of the former is strongly marked, and 

 on it the most typical halophytic formations depend — e.g., salt 

 meadows, salt marshes, and brackish-water vegetation. As for 

 the effect of sea-spray, it has probably been very much overesti- 

 mated. Quite recently T. H. Kearney (27) has shown this to 

 be the case for certain parts of the east coast of North America, 

 and he comes to the conclusion that dune plants, and even those 

 of the strand, for the most part do not owe their adaptations 

 against transpiration to excess of salt in the soil, but to other 

 conditions, and that they are rather ordinary xerophytes than 

 halophytes. 



The above explanation seems to meet New Zealand condi- 

 tions. Thus, the large shrubby nettle, Urtica ferox, is a common 

 maritime plant, growing in some instances on the upper strand 

 not far from high-water mark. But, as is well known, that 

 genus is one which is distinctly averse to salt in the substratum 

 (Warming, 44 ; p. 304). Macropiper excdsum, another frequent 

 coastal plant, belongs also to the same category. Mesemhrian- 

 themum australe, an extremely succulent plant, usually grows 

 on the face of cliffs, where salt could not penetrate to any extent. 

 The " coastal scrub " at the base of the Bluff Hill would most 

 certainly be non-existent were there excess of salt in the soil, 

 and yet some of its members overhang rocks covered with sea- 

 weeds. In short, the effect of spray seems to be largely depend- 

 ent upon the position of a formation with regard to the pre- 

 vailing wind, and upon the frequency and force of this latter. 

 And this brings me to the point that, in New Zealand at any 



