APPENDAGES OF THE STEM. 151 



Such functions are mainly instrumental in producing 

 a constant flow of sap upwards. In proportion to the 

 expanse, or quantity of foliage, in like proportion is 

 the need and consumption of water. Indeed their 

 hydraulic agency seems to be their chief office ; the 

 amplification of the plant could not take place with- 

 out such agency to assist the intestine impulse of the 

 swelling vessels. It has been observed that shoots 

 having leaves upon them, cut oif from the tree, 

 quickly wither ; but, if the leaves are taken oif, the 

 shoots will remain plump a much longer time ; a 

 proof of their transpiring powers. 



Although the leaves are attached to the bark before 

 as well as after their expansion, the connexion is only 

 temporary. Those of deciduous trees drop or wither 

 as soon as the summer growth is over. Some shrubs 

 and trees shed them in the second or third year, 

 hence they are called evergreens ; and the fir tribes 

 retain their foliage for many years. In the latter 

 case it seems their persistency is only owing to the 

 resinous consistency of the sap and suberous charac- 

 ter of the bark, or rather that they are not all 

 appended to buds as are those of other trees. In all 

 cases the attachment is not very intimate; there 

 being no connecting fibres or other vessels of a per- 

 manent character passing from one to the other ; all 

 such being articulated at the junction, except only 

 the palms, in the early stage of their growth, and all 

 other plants having what are called " spurious stems," 

 viz. stems chiefly formed of the permanent bases of 



