CH. II. 



COUKSE OF THE SAP. 



55 



younger brethren. It has then no case ; and it is a very 

 frequent rule, though with many exceptions, that those 

 leaves which have cases are either doubled or rolled on 

 themselves, and those leaves which have no cases are 

 folded over the remaining bud. 



Neither has the relative time at which the fruit-bud 

 or the shoot-bud hursts any reference to any general 

 chemical cause, but to the particular constitution of the 

 tree. For instance, the white-thorn, or May, develops 

 its leaves and shoots before its flowers ; the black-thorn, 

 or sloe, develops its flowers before its leaves and shoots. 

 And this last is perhaps the most general rule among 

 fruit-trees. Many, however, develop flowers and shoots 

 simultaneously. 



With regard to the death of the leaf at the time of 

 the ripening of the fruit, perhaps the only way in 

 which leaves have any reference to the growth or to 

 the ripening of the fruit is, that if there are too many 

 leaves, their increase abstracts from the growth of the 

 fruit, and their shade prevents the ripening of it. But 

 do summer apples and pears, or do the plants which 

 ripen their ft-uits in June and July, 'yield to the 

 chemical influence of the oxygen of the air,' and de- 

 foliate then? If so, cherry-trees would be curious 

 objects about midsummer ; so would gooseberries, 

 raspberries, currants, &c. Strawberries make their 

 great growth after ripening their fruit. 



Deciduous trees defoliate at the end of autumn, 

 though this is very much an afiair of temperature ; 

 that is, the same tree, in difierent latitudes, will keep 



