JUNE. 109 



waters, but examples can be found among many families ; 

 and our Idotea is a not uninteresting case. There is one 

 point on which further information is wanted, and that 

 is whether Dr Coppinger's specimens were found in fresh 

 water or in the sea. If in the latter, then it is probable 

 that our New Zealand forms have only recently acquired 

 the fresh-water habitat. But if the species occurs in fresh 

 water in Patagonia and Tierra del Fuego, then its occur- 

 rence in two such widely separate localities as New 

 Zealand and South America becomes a much more interest- 

 ing problem one related to the distribution of the tutu, 

 the genus Fvichsia, and that of various other forms of 

 vegetable and animal life. 



The usual plants, mostly of the sedge and pond-weed 

 families, which are to be found in all coastal lagoons, are 

 met with abundantly in that at Tomahawk. Some of 

 these are characterised as marking the border line between 

 fresh and salt-water plants. "While marine animals, as 

 I have said, are to be found in several instances invading 

 fresh water, it is very rare to find marine plants doing so. 

 On the other hand, a few fresh water flowering plants 

 appear to have acquired the power of growing first in the 

 brackish water of estuaries and then, gradually advancing 

 seawards, have adapted themselves to a marine habitat. 

 Some of these transition forms are to be seen in Tomahawk 

 Lagoon, as in other brackish- water localities along the 

 coast. In speaking of them I mvist use technical names 

 as they have no common or trivial names. Two forms 

 especially, Ruppia and Zannichellia, grow commonly 

 towards the seaward end of the lagoon. Rooted on the 

 bottom, their slender grass or thread-like stems and leaves 

 float upwards, seldom reaching the surface. Ruppia 

 exhibits a curious device in connection with its flowering 

 and fruiting. The flowers have both stamens and pistil, 

 and are probably quite capable of self-fertilisation. But, 

 as is usually the case with such plants, cross-fertilisation 

 is most likely beneficial to the race. So when the flowers 

 are ready to open their stalks lengthen to such an extent 

 as to float the flowers on to the surface of the water. 



