On the Propagation of Trees by Cuttings in Summer, 217 



young and immature leaves, on the contrary, vitiate the air in 

 which they grow by throwing off carbon; and they expend, in 

 adding to their own bulk, that which ought to be expended in the 

 creation of shoots. This circumstance respecting the different 

 operations of immature and mature leaves upon the surrounding 

 air, presented itself to the early labourers in pneumatic chemistry. 

 Dr. Priestly noticed the discharge of oxygen gas, or dephlo- 

 gisticated air, (as it was then called,) from mature leaves ; Scnr.i.i.i. 

 making, as he supposed, a similar experiment upon the young leaves 

 of germinating beans, found these to vitiate air in which they grew. 

 These results were then supposed to be widely at variance with 

 each other; but subsequent experience has proved both philo- 

 sophers to have been equally correct. 



I possess many young seedling trees of the Ulmus campestris, or 

 suberosa, or glabra, for the widely varying characters of my seedling 

 trees satisfy me that these three supposed species are varieties 

 only of a single species. One of these seedling plants presented a 

 form of growth, which induced me to wish to propagate from it. 

 It shews a strong disposition to aspire to a very great height with 

 a single straight stem, and with only very small lateral branches, 

 and to be therefore calculated to afford sound timber of great 

 length and bulk, which is peculiarly valuable, and difficult to be ob- 

 tained, for the keels of large ships ; and the original tree is growing 

 with very great rapidity in a poor soil and cold climate. 



The stem of this tree, near the ground, presented, in July, many 

 very slender shoots about three inches long. These were then 

 pulled off and reduced to about an inch in length, with a single 

 mature leaf upon the upper end of each, and the cuttings were 

 then planted so deeply in the soil, that the buds at the bases of the 

 leaves were but just visible above the surface of the soil. The 

 cuttings were then covered with bell glasses in pots, and put upon 

 the flue of a hothouse, and subjected to a temperature of about 80°. 

 Water was very abundantly given; but the under surfaces of the 



