VOL. XIII.} PHILOSOPHICAL TRANSACTIONS. 6ig 



therefore having 18 rings, one for each year; that which is made the last year 

 being always the greatest, though not always proportionably great, but accord- 

 ing as the year is more or less fruitful. The pieces described* in the following 

 figures are such as E-J- in the 15th ring, and sometimes not so large ; yet from 

 such a part I doubt not but the constitution of the whole tree may sufficiently 

 be understood. 



When a tree is sawed across, and afterwards planed very smooth, we see 

 lines J as it were drawn from the centre A, and reaching to the circumference 

 B; these are vessels which carry the sap to the bark ; as by the adjoined figures 

 will appear. 



In fig. 2, ABCD shows a piece of oak, which observed in a microscope was 

 thus drawn from a piece of wood as large as H. FF where the brown strokes 

 appear, are the separations of the growth of one year. For when the growth 

 stops, the wood becomes firm and thick; and is supplied with many small 

 vessels, such as are hardly to be distinguished, and therefore appear as brown 

 rays or streaks. Between the said FF, FF, is comprehended that thickness of 

 wood which has been added to the circumference of a tree by a year's growth. 

 The wood has five sorts of vessels, || viz. Three sorts going upwards, and two 

 lying horizontally. EEE denote large ascending vessels made every year in the 

 wood in the spring, when it begins to grow. These are filled within with small 

 bladders, which have very thin skins, here expressed in one of the greatest 

 vessels, cut longwise in the third figure by IKLM. The second sort of rising 

 vessels are much smaller, which also are made of very thin skins, and are also 

 specked with parts which by a common microscope appear like globules, as ON, 

 fig. 4, where one of the said vessels is cut longwise. The third sort of rising 

 vessels are very small, and in great number, being made also of very thin skins, 

 as PQ, fig. 4, where they are drawn longwise. 



All these ascending vessels in the aforesaid piece of wood, which is about -^ 

 of a square inch, are I guess about 20,000 vessels. Hence in an oak tree of 4 

 feet diameter are 3,200 millions of ascending vessels, and in one of 1 foot, there 

 are 200 millions of vessels. If we suppose 10 of these great and small vessels in 



* The same noted in Dr. Grew's Anatomy of Tranks, p, 24. — Orig. 



f Note the figures as they are here engraved are not so large as those designed by the author, being 

 sometimes but -^ (or other part) of their length ; and so must be supposed not to reach from ring to 

 ring as E. — Orig. 



X The same which Dr. Grew calls the insertions. Anatomy of Plants, chap. 2. And diametral 

 rays. Anatomy of Tr. p. 20, 50, &c. — Orig. 



n See a figure of the same wood with all the same five parts, in Dr. Grew's Anat. of Plants. 

 And the partitions of the great horizontal parts, hereafter mentioned, see in his Anat. of Roots 

 tab. 7. — Orig. 



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