140 TILLEES OF THE GEOUKD CHAP. 



We have already spoken of the great import- 

 ance in hot countries of such fruits as bananas, 

 dates, and figs, all of which contain a considerable 

 amount of food material. We must remember also 

 that vegetable marrows, pumpkins, cucumbers, and 

 so on, are all fruits to the botanist, and these are 

 very useful in warm countries as important additions 

 to the diet. 



The fruit of the olive tree, again, as we have 

 seen, yields the kind of fat which is most suitable 

 to people in hot climates. 



CHAPTEE XII 



IMPROVING CULTIVATED PLANTS 



WE have already seen that most of our cultivated 

 plants are very old, and that with regard to many, 

 we do not even know from what wild plants they 

 were derived. If, however, the beginnings of these 

 useful plants are very old, we know, on the other 

 hand, that great improvements in them have been 

 made in relatively modern times. Nearly all our 

 cultivated plants now occur in a great number of 

 varieties, fitted for different soils or different 

 countries, yielding different kinds and amounts 



