BOTANIC GARDENS. 177 



light, and only a comparatively small addition may thus be made 

 to the flora of a garden. The conditions described above are such 

 that it has not been found possible to grow in one place more 

 than fifteen thousand species of the higher plants. It will be 

 found, moreover, that a large number of the species included are 

 not able to attain normal stature and appearance, and will thus be 

 useless in representing the form intended. 



In consequence of this limitation of the number it is custom- 

 ary to supplement the living plants by collections of prepared 

 specimens of contemporaneous and fossil forms, in order to rep- 



The Main Palm House of the Royal Gardens at Kew, with Lake in Foregeound. 



resent more completely the vegetation of the globe. The living 

 as well as the prepared plants are generally so assembled as to 

 demonstrate the descent and relationship of the different groups, 

 distribution over climatic and geographic zones, as well as their 

 principal biological adaptations to the factors to be met in their 

 native habitats. In addition to this strictly natural method of 

 treatment it is also customary to illustrate by proper groups the 

 forms which have become of special interest because of their food- 

 furnishing, textile-yielding, medicinal, or other economic value. 

 In order to accomplish these purposes a suitably equipped garden 

 must contain, besides the necessary facilities for growing plants, 

 museum buildings arranged for the display of prepared specimens, 

 and if it designs to afford opportunities for research it must also 

 be furnished with a library and laboratory facilities. 



There are in the world more than two hundred institutions 

 designed as botanic gardens, a large proportion of which are de- 

 voted to the cultivation of decorative plants, or subserve the use 



