xi CHIEF KINDS OF FOOD-PLANTS 137 



are sometimes poisonous. We have all eaten 

 apples, and we have all been told, since we were 

 quite small, that it is not wise to eat apple pips. 

 Suppose we try one, however ; it will not do us 

 much harm, and it is an interesting experiment. 

 If we nibble it slowly between our teeth, we find 

 that our mouths become filled with a nasty-tasting 

 substance. If we eat two or three pips, this nasty 

 taste will perhaps remain in our mouths for several 

 hours, and give us a very uncomfortable sensa- 

 tion. But when apples appear on the table at 

 dinner-time, after having been baked or stewed, 

 we find that the pips have no taste at all, and 

 do not disagree with us. This means that, in. 

 cooking, the heat of the fire has driven off the 

 poison. 



Now, it is not at all uncommon to find that 

 parts of plants contain poison, which protects them 

 against the attacks of plant-eating animals. But 

 man is cleverer than the animals, and he learnt 

 long ago that poisons could often be driven off by 

 heat. In Brazil the people live very largely on 

 manioc, and it is full of a deadly poison. What 

 do they do ? Well, the roots, the edible parts, are 

 first carefully scraped, then the interior is crushed 

 into a kind of flour, and carefully baked in thin 

 layers, so as to drive off the poison. Prepared in 

 another way manioc makes tapioca, which we eat 



