i893. NOTES AND COMMENTS. 247 



mode of life of pelagic forms : it secreted slime to gather together the 

 small organisms in the intaken sea-water. The gradual change of 

 function of any organ is a biological problem of vast interest, and here 

 seems a case to be dealt with by the morphologist and the physiologist 

 liand in hand. 



The Polynesian Islands. 



Under the title of Flora of French Polynesia, M. Drake del 

 Castillo gives a systematic account of the Flowering Plants and Ferns 

 which grow spontaneously or are generally cultivated in the Society, 

 Marquesas, Pomoton, Gambler, and Wallis Islands. The Society 

 Islands are by far the most important, whether we consider extent, 

 population, and productions, or flora, and of these Tahiti holds the 

 first rank. 



With but slight differences, the climate of French Polynesia is the 

 same as that of the other Polynesian islands. In the Society Islands, the 

 mean annual temperature is a little above 75° F. The year is divided 

 into two seasons of almost equal duration, determined by the direction 

 of the Avind. From August to October a S.E. wind, called Maarama 

 by the natives, prevails, and the weather is rather dry, though storms 

 are not rare. A N.E. wind rules from November to March, and rains 

 are frequent. However, the difference between the two seasons is not 

 strongly marked, and it rains more or less during the whole year. The 

 climate is moister in the high valleys than near the shore, and there 

 is a corresponding difference between the vegetation of the two regions, 

 while the eastern side being more exposed to the storms brought by 

 the S.E. winds, the limit of the humid zone is lower than on the 

 western side. 



The Marquesas are drier than the Society Islands. These 

 conditions of climate necessarily produce a luxuriant vegetation, which 

 is, however, more brilliant than varied, and remarkable more for the 

 development in number of individuals than species. The poverty of 

 the flora chiefly consists in a want of special forms, a characteristic of 

 small islands. Annuals are poorly represented, almost two-thirds of 

 the whole vegetation consisting of small perennial shrubs, while trees 

 and large shrubs constitute another third. This predominance 

 of shrubby plants is explained by the nature of the soil. On the 

 abrupt sides of the valleys, woody plants with short stems and 

 vigorous roots, and ferns with creeping rhizomes, are almost the only 

 kinds which can profit by the scanty support afforded by the soil. 

 Tall trees occur for the most part only in the lower valleys or in the 

 ridges. Feebler plants can only get on by the help of their neigh- 

 bours, which they use as supports or hosts; hence it comes that 15 

 per cent, of the vascular plants are climbers, parasites, or pseudo- 

 parasites. The few herbs live on the borders of streams or dry hills. 

 Owing to its rocky nature and steep slopes in the mountainous islands, 

 the soil retains but little of the large amount of water it receives, 



