HO OBSERVATIONS ON THE STATE OF THE 



the true, or peculiar juice, or sap of the plant. Whence this fluid origi- 

 nates does not appear to have been agreed upon by naturalists ; but I have 

 offered some facts to prove that it is generated by the leaf* ; and that it 

 diners from the common aqueous sap owing to changes it has undergone 

 in its circulation through that organ : and I have contended that from 

 this fluid (which Duhamel has called the sue propre, and which I will 

 call the true sap) the whole substance, which is annually added to the 

 tree, is derived. I shall endeavour in the present paper to prove that 

 this fluid, in an inspissated state, or some concrete matter deposited by 

 it, exists during the winter in the alburnum, and that from this fluid, or 

 substance, dissolved in the ascending aqueous sap, is derived the matter 

 which enters into the composition of the new leaves in the spring, and 

 thus furnishes those organs, which were not wanted during the winter, 

 but which are essential to the further progress of vegetation. 



Few persons at all conversant with timber are ignorant, that the 

 alburnum, or sap-wood of trees, which are felled in the autumn or winter, 

 is much superior in quality to that of other trees of the same species, 

 which are suffered to stand till the spring, or summer : it is at once more 

 firm and tenacious in its texture, and more durable. This superiority in 

 winter-felled wood has been generally attributed to the absence of the 

 sap at that season ; but the appearance and qualities of the wood seem 

 more justly to warrant the conclusion, that some substance has been 

 added to, instead of taken from it, and many circumstances induced me 

 to suspect that this substance is generated, and deposited within it, in 

 the preceding summer and autumn. 



Duhamel has remarked, and is evidently puzzled with the circum- 

 stance, that trees perspire more in the month of August, when the leaves 

 are full grown, and when the annual shoots have ceased to elongate, than 

 at any earlier period ; and we cannot suppose the powers of vegetation to 

 be thus actively employed, but in the execution of some very important 

 operation. Bulbous and tuberous roots are almost wholly generated after 

 the leaves and stems of the plants to which they belong have attained 

 their full growth : and I have constantly found, in my practice as a 

 farmer, that the produce of my meadows has been immensely increased 

 when the herbage of the preceding year had remained to perform its 

 proper office till the end of the autumn, on ground which had been mowed 

 early in the summer. Whence I have been led to imagine, that the 

 leaves, both of trees and herbaceous plants, are alike employed, during 

 the latter part of the summer, in the preparation of matter calculated to 



* See above, Paper No. III. 



