ACCOUNT OF SOME EXPERIMENTS ON THE 



Were a tree capable of affording an eternal succession of healthy 

 plants from its roots, I think our woods must have been wholly overrun 

 with those species of trees which propagate in this manner, as those scions 

 from the roots always grow in the first three or four years with much 

 greater rapidity than seedling plants. An aspen is seldom seen without 

 a thousand suckers rising from its roots ; yet this tree is thinly, though 

 universally, scattered over the woodlands of this country. I can speak from 

 experience, that the luxuriance and excessive disposition to extend itself 

 in another plant, which propagates itself from the root (the raspberry), 

 decline in twenty years from the seed. The common elm being always 

 propagated from scions or layers, and growing with luxuriance, seems to 

 form an exception ; but, as some varieties grow much better than others, 

 it appears not improbable that the most healthy are those which have last 

 been obtained from seed. The different degrees of health in our peach 

 and nectarine trees may, I think, arise from the same source. The oak 

 is much more long-lived in the north of Europe than here ; though its 

 timber is less durable, from the number of pores attending its slow 

 growth. The climate of this country being colder than its native, may, 

 in the same way, add to the durability of the elm ; which may possibly be 

 further increased by its not producing seeds in this climate, as the life 

 of many animals may be increased to twice its natural period, if not 

 more, by preventing their seeding. 



II. ACCOUNT OF SOME EXPERIMENTS ON THE ASCENT OF THE SAP IN 



TREES. 



[Read before the ROYAL SOCIETY, May Uth, 1801. ] 



THESE experiments were made on different kinds of trees ; but I shall 

 confine myself to those I have made on the crab-tree, the horse-chestnut, 

 the vine, and the oak ; and shall begin with those made on the crab-tree. 



Choosing several young trees of this species in my nursery, of something 

 more than half an inch diameter, and of equal vigour, I made two 

 circular incisions through the bark, round one half the number of them, 

 about half an inch distant from each other, early in the spring of 1799 ; 

 and I totally removed the bark between these incisions, scraping off the 

 external coat of the wood. The other half I left in their natural state. 



At the usual season, the sap rose in equal abundance in all ; and their 

 branches shot, during the whole spring, with equal luxuriance. But that 

 part of the stems (of the trees whose bark had been taken off) which was 



