270 PHYSIOLOGY OF TREES. 



them ; witness the early movements of bulbs and 

 amentaceous plants. 



Trees and shrubs are individuals as far as they 

 have a pith, bark, and a covering of vitality in 

 common, but dividuals in so far as they are 

 divisible both by nature and art: naturally by 

 seeds and suckers : artificially, by cuttings, bud- 

 ding", grafting, and layering. In all cases, the 

 organisation and increments proceed from the 

 cambium, as has been repeatedly stated ; and 

 as vegetable life is no other than the develop- 

 ment of pre-existing organisation, we must 

 allow that there must be some connecting mem- 

 branes which unite the parts with the whole. 

 The equivocal generation of plants, or even parts 

 of plants, is not more absurd than is the equi- 

 vocal generation of animals, 



I am quite aware that questioning the validity 

 of this old idea, viz. the descent of the sap, will 

 meet the opposition of many very experienced 

 men, both scientific and practical : even the wood- 

 man will remonstrate, and triumphantly ask why 



