TALL OF THE LEAF. 26l 



any body else, who endeavours to explain the physio- 

 logy of vegetables or of animals according to one prin- 

 ciple only, whether it be mechanical or chemical, 

 should entirely fail. To consider the fall of leaves in 

 autumn as a sloughing, or casting off diseased or worn 

 out parts, seems so simple and evident, as to be hardly 

 worth insisting upon. Yet I find myself anticipated in 

 this theory by one physiologist only, named Vrolick, 

 cited by Willdenow, in his Principles of Botany, 

 p. 304, though several learned speculations -to no pur- 

 pose are extant on the subject. It is but just, however,, 

 that I should relate what led me to consider the matter 

 with any attention. My observing friend Mr. Fairbairn 

 of Chelsea garden long ago remarked to me, that when 

 he had occasion to transplant any tree or shrub whilst 

 in leaf, he could soon judge of its success bj the ease 

 with which its leaves were detached. The consequence 

 of such treatment is more or less injury to the health 

 of the plant, as will first appear by the drooping of 

 the leaves, most of which will probably die, and the 

 decay will generally be extended to the younger more 

 delicate twigs. The exact progress of this decay may 

 speedily be known, by the leaves of those branches 

 which are irrecoverably dying or dead, remaining 

 firmly attached, so as not to be pulled off without a 

 force sufficient to bring away the bark or buds along 

 with them : whereas the leaves of parts that have re- 

 ceived no material injury, and where the vital energy 

 acts with due power, either fall off spontaneously or 



