T36 NATURAL SCIENCE. August, 



be submerged are indicated. The book is not one which can be 

 summarised ; but it may be recommended as a useful, concise and 

 accurate sketch of the geography and ethnology of Northern Africa. 

 The maps are especially worthy of commendation. 



J. W. Gregory. 



Distribution of Plants. 



Plantesamfund. Grundtraek af den Okologiske Plantegeografi. AfEug. Warming, 

 Professor i Botanik ved Kjobenhavns Universitet. 8vo. 335 pp. 



This new work by Dr. Warming constitutes a most original contri- 

 bution to the study of the distribution of plants. According to his 

 conception the problems of plant-geography present themselves under 

 two distinct heads, the Floral and the CEcological. The first has been 

 already treated, notably by Grisebach and Drude, but hitherto there 

 has been no text-book dealing with the " (ecological" (oikos, Ao'yos) 

 aspect of the subject. In a consideration of Floral Plant-geography, 

 the first and most important point is to determine a catalogue of the 

 plants inhabiting definite areas, and the next to divide the areas 

 into floral districts, based upon the relationship of the species and 

 genera, and leading to a division of the areas into natural regions ; 

 following this there is the determination of the boundaries for species 

 and genera, their distribution and relative numbers in various 

 countries, the consideration of endemic forms, the relation of Insular 

 Floras to those of the mainland, and of Mountain Floras to lowlands, 

 etc., etc. 



CEcological Plant-geography deals with quite another problem, it 

 treats of the laws and influences affecting the forms and characteristic 

 groupings of plants, and seeks to teach us how the external appearance 

 and internal economy (Jmsholdning) of plants and plant-communities 

 {plantesamfund) are regulated according to the supply of warmth, 

 light, nutriment, water, etc., which is at their command. A hasty 

 glance suffices to show that species are not evenly distributed over 

 the districts which compose their zone, but are grouped into com- 

 panies with very varied physiognomy. The first problem suggested 

 is to find out what species are confined to localities of a homogeneous 

 character. The next, and very difficult one, is a solution of the 

 questions : Why they are confined in distinct groups, and why these 

 have their pecuUarly distinctive features. This leads on to a con- 

 sideration of questions relating to the internal economy of plants, 

 their requirements according to the conditions under which they 

 live, the manner in which they utilise the external conditions at 

 their command, and adapt themselves to these in their structure and 

 physiognomy, and especially to considerations of the " Forms of 

 Life." 



These are some of the complex questions to which Dr. Warming 

 addresses himself. The scheme he adopts in his book is to divide it 

 into sections : the first section treats of the factors which play a part in 

 the interna] economy of a plant and the influence these exert upon both 

 the external and internal forms, upon the duration of life and other 

 biological facts, as well as upon the topographical limitation of the 

 species : the second treats of the arrangement into a system and the 

 characteristics of the communities or "social classes" which are found 

 upon the earth — Hydrophytous, Xerophytous, Halophytons, and Mesophytous 

 vegetations ; and the third of the struggle between the different 

 communities. In the first section the various factors and their 

 influences are considered in turn, although, as is pointed out, these 



