l] WHAT IS PLANT GEOGRAPHY ? 3 



the Greek word (pvror, a plant), accordingly deals with the plant 

 cover of the world — with its composition, its local productivity, and 

 particularly its distribution. This matter of distribution should be 

 tackled both on the separate basis of individual species, etc., and 

 collectively by dealing with their various and complex assemblages 

 that make up vegetation. Our object will be to describe and inter- 

 pret all we can of the manifestations of plant geography, paying 

 special attention to the differences and similarities existing between 

 the various floras and vegetations of the world. The continued 

 increase in total human population makes such a study vitally 

 significant, Man being dependent on plants for the very where- 

 withal of his existence. 



The economic importance of our subject stems from the fact that 

 green plants alone, on any substantial scale, are able to build, from 

 simple raw materials and energy derived from sunlight, the complex 

 substances on which animals as well as the plants themselves all 

 depend for food. This food constitutes the main source of material 

 used in body-building, and in it is locked the energy required for 

 the various processes of life. Animals, with their usually active 

 existence, commonly need this energy in abundance. In them, as 

 in plants, it is liberated by the process of respiration, which is a 

 kind of slow burning that takes place in living matter and gives to 

 Mammals and Birds their bodily heat. Green plants provide food 

 for us directly, when we eat them or their products, or indirectly, 

 when we eat animals that fed on plants or were at least ultimately 

 dependent upon some form of plant life, as indeed all are. 



Plants also provide us with much of our clothing and housing as 

 well as industrial raw materials, while in the world as a whole they 

 largely condition our environment — forests, for example, being clearly 

 different to live in from grassy plains or desert oases. Indeed, 

 many of the major migrations of Man and other animals have been 

 primarily due to plant distribution. Plants constitute for mankind 

 the main inexhaustible source of fuel and industrial supplies and 

 are of fundamental importance in many different branches of 

 industry : in drug production, brewing, pulp and paper making ; 

 in lumbering, in the textile industries, in tanning, dyeing and curing ; 

 in the production of plastics, animal feedstuffs, scent, oil, rubber, 

 resin, gum, wax and fibres ; and, of course, in the wider fields of 

 agriculture, horticulture, forestry, fish-culture, and the direct uses 

 of their innumerable products. 



It can be seen from the contents of the earlier works listed at 



