128 VEGETABLE SAP. 



mystery ; but as it is easily proved that cambium 

 and sap are two very different components of the 

 plant, and moreover that no direct proof has yet been 

 had of the descent of fibrous matter from the buds 

 downward, we are compelled to pause before we can 

 confidently ascribe the cause of the tumours to either 

 the descent of the sap, or to ligneous fibres from the 

 superior buds. 



But if neither sap nor fibrous matter produce those 

 appearances, what else can it be ? We have already 

 said, that the circumstance is inexplicable ; and it 

 would be uncandid and inconsistent with our regard 

 for truth, did we not frankly acknowledge our ina- 

 bility to explain the phenomenon. Mere supposi- 

 tions would be impertinent ; and it is, every way better 

 to leave such a matter open by recommending it to 

 the consideration and scrutiny of others, than obscure 

 it by fanciful conjectures. 



The only circumstances which appear analogous 

 to the downward action observable in this case, are, 

 firstly, the manner of flowering of the genus Liatris. 

 and some other plants. Instead of the flowers opening 

 from the bottom of the stem upwards, they begin at 

 the top, and blow consecutively downwards. Secondly, 

 the culms of wheat, and other corn ripens, or rather 

 dies, from the ear downwards ; so that the seeds are 

 ripe before the vital action ceases at the bottom, and 

 whilst the crown is yet throwing up fresh stems. 

 Thirdly, the spring motion of the sap begins at the 

 points of the branches. This fact has led some most 



