REVIEWS 527 



floras of the coastal districts. Go almost where he may, he finds the sandy shore 

 occupied by a characteristic association of plants several of the members of which 

 are cosmopolitan. The long trailing stems of Ipomea biloba (closely related to 

 the Convolvulus Soldanella of our own shores), the bean Canavalia obtusifolia, 

 the prickly Ccesalpinia Bonducella, Morinda citrifolia, Hibiscus tiliaceus, Cocos 

 nucifera (the coco-nut palm), are equally characteristic of sandy beaches in 

 Ceylon, the Malayan region, the West Indies, tropical South America and parts 

 of Africa and Australia. 



On a muddy shore and in estuaries, the assemblage characteristic of the sandy 

 beach is usually replaced by another equally well marked plant association, the 

 Mangroves, some of the members of which are similarly widely distributed through 

 the tropics of both hemispheres. The general aspect of the mangrove swamp is 

 surprisingly similar, whether it is developed on a comparatively small scale in the 

 estuaries of Ceylon or the West Indies, or on the grand scale in a West African 

 delta region, where it is possible to steam for miles in an ocean-going liner 

 through typical mangrove forest. 



We might expect to find some break in the uniformity on visiting isolated coral 

 atolls or remote oceanic islands which have never been connected with a great land 

 mass. This, however, is not the general case, and the shores of these islands are 

 inhabited by many of the same species of plants. The majority of these coastal 

 plants have fruits or seeds which have considerable buoyancy enabling them to 

 traverse wide areas of ocean. Some germinate and establish themselves on 

 reaching a suitable resting-place. For our knowledge of the methods of dispersal 

 of these interesting plants we are largely indebted to the well-known researches of 

 Schimper and Guppy. The best practical demonstration was afforded, however, by 

 the reorganisation of Krakatau after the famous eruption of August 1883. On that 

 occasion a portion of the island was completely blown away and the remainder 

 covered with lava, to the destruction of all living beings. Treub visited the island 

 in 1886 and recorded the colonists which had already arrived. Prof. Ernst brings 

 our knowledge of events up to date, and by the aid of excellent photographs 

 presents a vivid picture of the state of affairs to-day when " twenty-five years since 

 the complete destruction of all organic life on the group of islands, these are again 

 covered by a mantle of green, the growth being in places so luxuriant that 

 it is necessary to cut one's way laboriously through the vegetation." 



All divisions of the plant kingdom are now represented on Krakatau, the total 

 list of species being 137. Of the plants of the shore no less than two-thirds 

 are species ubiquitous on tropical coasts. The author tabulates observations 

 regarding ocean currents, prevalence of winds and other data, and his researches in 

 conjunction with those previously made afford very full knowledge regarding this 

 aspect of the colonisation of an island and of the dispersal of tropical shore plants. 

 Especially interesting is it to find that the coco-nut palm has established itself, 

 as the power of this plant to do so has been denied. 



Birds and air currents have also played very important parts in the restocking of 

 the island. Treub in his early visit showed conclusively that an inland and a 

 littoral flora were being formed independently and concurrently. To these 

 observations Prof. Ernst has added considerably ; of especial interest to others 

 beside botanists is his account of the manner in which the blue-green algaa 

 (Cyanophyceae), bacteria and moulds have played their part in the preparation of 

 a favourable substratum for the higher plants. Prof. Schwarz in his article on 

 " The Organisms of the Soil " (Science Progress, 1909, 4, 153) refers to the fact 

 of Treub finding as early as 1886 that these blue-green algas were the first to 



