34 LETTEIt II. 



you have already been told that poisons, when it is 

 the nature of plants to yield poisons, are also formed 

 in leaves by the action of lioht ; the absence of this 

 wonderful agent will therefore prevent the formation 

 of poison, as well as the formation of green colour ; 

 and hence blanching renders poisonous plants harm- 

 less. Thus, in the Celery, but a small portion only 

 of the leaves is exposed to light ; the whole of the 

 stem and of the lower part of the leaves is buried in 

 the earth ; the small quantity of noxious matter that 

 might be formed by the few leaves which are allowed 

 to bask in the sun, has to pass down the buried 

 stalks of the leaves before it can reach the stem, 

 where it would be laid up ; but you know the leaf- 

 stalk of the Celery is very long, and any thing 

 which has to filter from the upper part of such a leaf 

 to its bottom has to take a long journey, in the course 

 of which it is constantly under the destroying influ- 

 ence of darkness ; so that before it can reach the 

 stem, it will all have perished. A similar effect 

 is produced by the Italians upon Fennel, which, 

 although not a poisonous plant, has too powerful a 

 taste to be a pleasant food, except as an ingredient 

 for flavouring sauces. The Italians, in their warm 

 climate, cause Fennel to grow rapidly in darkness, 

 and thus obtain it in a state very like Celery in 

 appearance ; the darkness destroys the principal 

 part of the flavour, no more of the Fennel taste 

 being left than is sufficient to give the blanched 

 stems a pleasant aromatic quality, 



There are no plants which you are likely to mis- 



