248 NATURAL SCIENCE. Oct., 



while the narrow deep valleys keep the air constantly charged with 

 moisture. Thus, if the roots absorb little, the leaves exhale but little, a 

 fact which explains the chartaceous or coriaceous nature of the foliage 

 of many species. 



M. Castillo remarks that the flora of French Polynesia is a poor 

 one, containing, according to our present knowledge, only 588 species 

 of vascular plants distributed among 79 families, and representing 262 

 genera. They are classed under three headings. First, species con- 

 fined to the islands, numbering 161 ; secondly, species distributed 

 throughout Oceania, 123 ; and thirdly, comprising a half of the flora, 

 or 297 species, those which are also found in the Indo-Malayan 

 region. The predominating families are, Ferns, Leguminosae, Orchids, 

 Rubiaceae, Grasses, Cyperaceae, Euphorbiaceae and Urticaceae. The 

 predominance of ferns — with their light and easily-carried spores — over 

 the less easily dispersed flowering plants is a well-known charac- 

 teristic of insular floras, consequently it is not surprising to find this 

 group represented by as many as 142 species, or nearly one-fourth of 

 the whole. There are 37 species of Leguminosae, 34 Orchids, 31 

 Rubiaceae, and 30 Grasses. A Freycinetia is specially mentioned as 

 very plentiful and covering large areas, and along with the plaintain 

 (Musa paradisiaca), a plant of a very different type, recalling the vege- 

 tation of a Malay or East Indian jungle. 



Lake Vegetation. 



Ix two recent numbers (nos. 54 and 55) of the Revue Generate de 

 Botaniquc, A. Magnin discusses the vegetation of the lakes of Jura. 

 After exploring a number of lakes, the regularity with which the 

 plants are distributed becomes very striking. Passing from the shore 

 to the centre, distinct zones are noticed somewhat as follows. 



1. A littoral zone of reeds (P/iragjiiites communis) and bulrushes 

 (Scirpus lacustris), which stand out of the water. Sometimes the two 

 plants are more or less intermingled, but usually the reeds alone line 

 the shore, forming the Phvagmitetum, extending to a depth of 2-2^ 

 metres, while the bulrushes form a second ring, or Scirpetum, to a depth 

 of 3 metres, a mixed zone uniting the two. Sometimes the order is in- 

 verted through the formation of a bar beyond the shore, the reeds in- 

 stalling themselves in the shallower water. Besides these, where the 

 water is shallow, sedges, Phellandrium, Equisetum limosum, and others are 

 observed, as well as some plants with swimming leaves, like Polygonum 

 amphibium, the white water-lily (Nympha .talba), and Potamogeton nutans. 



2. Beyond the bulrushes plants with stems standing out of the 

 water are no longer found, but only those with swimming or floating 

 leaves. Especially characteristic of this zone is the yellow water-lily 

 {Nuphav tulcum), which occurs in almost all the lakes of the Jura, 

 frequently forming a large continuous girdle, or great patches, from the 

 limit of the scirpetum to the edge of the first slope to a depth of 3-5, 



