224 LIGHT, VEGETATION AND CHLOROPHYLL 



Botanical geographers could make an inventory of our 

 resources in vegetation and of their distribution over the 

 earth's surface. It may be possible to increase and exploit 

 some neglected species, or to spread others that have been 

 confined to only a small area. 



Plant biology has achieved magnificent results. All the 

 resources of genetics have been brought into use; difi'erent 

 varieties have been crossed to concentrate in one single 

 variety the greatest possible number of qualities, to ehminate 

 some hereditary characteristic which, in a given environment 

 makes a particular variety deUcate and fragile. A certain 

 pecuharity, favourable in one place, may be a disadvantage 

 elsewhere; it is necessary to experiment at length and select 

 unremittingly. 



By this patient work, lands formerly barren are becoming 

 fertile and cultivation steadily advances towards the poles 

 or the tropics. To give only one example, wheat is now cul- 

 tivated in every continent and in nearly all latitudes, so that 

 there is not a month in the year when, in one country or 

 another, harvesting is not in progress. By the skill of agri- 

 cultural botanists in selection, ever more varied plants multiply, 

 develop and adapt themselves to our needs. 



Soil-less culture, too, opens up new horizons; for example, 

 plants cultivated in nutrient solutions enabled American 

 troops to be supplied with fresh vegetables on desert islands 

 where almost everything was lacking, except sunshine. Better 

 still, lakes and seas are engaging the attention of botanists, 

 who are already thinking of promoting the development of 

 algae to feed certain species of fish. They are beginning to be 

 interested in a green alga, the unicellular chlorella, which 

 multiples so rapidly that it would be possible, by cropping it 

 every day, to obtain an abundant supply of substances rich in 

 albumins and even in Upides that the food industry could use. 



