76 



LETTERS ON TREES. 



but preserved in perpetuity^ — although (from accidental 

 causes, however, as explained in the preceding letter), 

 the original tree will not and cannot continue to last 

 for ever. The late Mr Knight, indeed, as is well 

 known, maintained the contrary. Participating in the 

 popular belief that there is a fixed period of life for 

 every tree, and one common period of death for all its 

 parts, he held that a young shoot taken from an old 

 tree could live only as long as the tree, and would die 

 with it, i. e. supposing that it died from natural causes. 

 In this way he accounted for the disappearance, or at 

 least the scarcity of several once well-known fruit- 

 trees, such as the Bed-streak and the Golden-pippen. 

 His views, however, have not been confirmed by the 

 observations and the experience of others. The fact 

 which he thus endeavoured to explam has been shewn 

 to be exceptional, and referable when it does obtain to 

 an entirely different principle.* 



14. Similar remarks to those now made in regard 

 to grafting apply to the analogous processes of pro- 

 pagation by slips or layers, and to the indefinite mul- 

 tiplication and endless perpetuation of such trees (the 

 Willow, for example) as admit of being reproduced in 

 that way. It is observed by Professor Henslow, that 

 all the Weeping-willows in Europe are said to have 

 been derived from cuttings taken from a single tree, 



^ Balfour, Class-Book of Botany, pp. 665-8. See also Letter 

 xvii. section 8. 



