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nurseries, which T afterwards formed, and which shall be 

 treated of in the sequel, had, at this period, no existence, and 

 the manifold advantages, since derived from them, were not 

 then contemplated. Still a sufficient variety of plants, both 

 in form and species, were obtained, so as to enlarge expe- 

 rience, and render the steps of its progress more interesting, 

 and its results more satisfactory. 



In these circumstances, I was naturally incited to inquire 

 into the causes of such unexpected phenomena, to engage 

 in the study of the anatomy of trees, and of vegetable phy- 

 siology, or the doctrine of the constitution and properties of 

 plants. And in respect to trees it is remarkable, that little or 

 nothing was known of this science in Europe, until the close 

 of the seventeenth century, when the first probable theory of 

 the circulation of the sap was discovered. Indeed, it is only 

 within the last forty or fifty years, that the science has been 

 greatly cultivated in Britain : and it will be admitted as a 

 striking proof of the fact, that, at this moment, few persons 

 comparatively, and, what is still more surprising, few planters, 

 are aware of the twofold course of the sap in trees, or of the 

 method in which their juices are either elaborated or cir- 

 culated. These studies, I found, threw great light upon the 

 subject. Appearances, for which I had not been able pre- 

 viously to account, were now satisfactorily explained ; and 

 means were suggested for obviating difficulties, that other- 

 wise seemed insurmountable. 



It has been already stated, that there are four distinct ex- 

 ternal provisions, termed the protecting properties, which 

 nature gives to trees in open exposures, and which distinguish 

 them from others, standing in the interior of woods. The 

 use of these properties is to enable trees to develop their ex- 

 istence vigorously, in spite of the external conditions, which 

 are unfavourable to such development. Which of the four 

 properties is really the most important for that purpose, it 

 was not easy to determine, as they are all relative and cor- 



