illustrating the Distribution of Plants. 19 



Now what is the best manner of constructing such maps, 

 or any diagrams in substitution ? this being the essential point. 

 Before replying to the question, we should call to mind the 

 different matters which it may be wished to represent, and the 

 degree of precision to be sought in such representation. It 

 may be wished to display the distribution of individual forms 

 known as species and varieties, or the groups of technical bo- 

 tany called orders and genera ; or the object may be to 

 exhibit the local physiognomy of vegetation en masse, in con- 

 nection with differences of climate, physical configuration, soil, 

 &c. The maps will vary accordingly. 



To represent the distribution of individual forms or species, 

 let us first imagine a common geographical map, in outline, 

 of such dimensions as would render it possible to mark 

 every locality for any given species, by some sign, or spot of 

 colour, covering a corresponding space of the map. This 

 would give an exact picture of the topographical distribution ; 

 but, as it would require to be made on the scale of at least a 

 yard to the mile, it is obviously quite out of the question. 

 With less precision, though still keeping sufficient exactness 

 for useful purposes, we might greatly reduce the scale by in- 

 dicating all localites within certain distances of each other as 

 single ones, the distances depending on the size of the map. 

 In maps on a very small scale, localities many miles asunder 

 would necessarily be reduced to units, and single stations of 

 trifling extent would be exaggerated, much as we see the 

 breadth of rivers, roads, and canals in ordinary maps. On 

 botanical maps of this kind, the political divisions and names 

 of places might be given, or omitted, as found convenient. 

 Another mode of representing the distribution of species, 

 would be by an outline map, in which the only places named 

 should be those where the species was known to grow, larger 

 or small topographical divisions (townships, parishes, coun- 

 ties, &c.) being adopted according as the species was more or 

 less generally diffused. Additional information respecting the 

 greater or less abundance of the plant, its claims to be con- 

 sidered native, and the authority for its existence in the places, 

 might be conveyed by a corresponding variation in the size or 

 character of the letters composing the names, as usually done 

 to distinguish cities, towns, and villages. In these cases, a 

 map would require to be devoted to each species, and the cost 

 be very great. 



But it is by no means impossible to give a general sketch of 

 the distribution of several species by means of a single map, 

 though precision of detail must be sacrificed if many are in- 

 troduced into the same map. To convey pretty full details of 



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