BO Rev. P. Keith on the Pith of Plants. 



altogether, or nearly, dry. They add, that the fact of the great 

 discrepancy of dimension between the pith of the primary 

 shoot of the elder and that of the shoots of after years, so 

 often quoted as an evidence of the shrinking of the pith, is an 

 argument founded altogether in error, as the pith of the pri- 

 mary shoot from seed never was more than a mere thread*. 

 Yet the question is not whether the pith of the shoot of future 

 years does ever shrink to the diminutive size of the shoot 

 of the first year from seed ; but, rather, whether the pith of 

 any shoot, be it primary or be it secondary, does ever shrink 

 in any sensible or perceptible degree after the end of a year's 

 growth, when its juices, as it seems, may be said to be ex- 

 hausted. On the 1st of June, 1836, I separated from the 

 stool of an ash-stock a stem of three years growth. It mea- 

 sured about nine feet in height, the growth of each year being 

 distinctly marked, and measuring each about three feet in 

 length. The upper shoot, that is the shoot of 1835, had a 

 diameter of fths of an inch, with a pith of ^th at the widest. 

 The middle shoot, that is the shoot of 1834, had a diameter 

 of T 7 2 ths of an inch, with a pith of £ th ; and the lower shoot, 

 that is the shoot of 1833, had a diameter of Jths of an inch, 

 with a pith of ygth. Now as the shoots of the several years 

 w 7 ere equally luxuriant, and the youngest a year old, the pith 

 ought, by hypothesis, to have been of the same dimensions in 

 all of them. Yet it was gradually smaller and smaller from 

 the youngest to the oldest ; though it was undoubtedly of 

 equal diameter in the first year's growth of each. For the 

 shoot of a single year, from a different stock, gave a diameter 

 of pith equal to that of the upper shoot of the above stem ; 

 and poles of twelve years old gave still a diminishing dia- 

 meter when inspected towards the base. Whence we infer 

 that the pith keeps shrinking, from one cause or other, long 

 after the period of the first year's growth. 



Since the above was written, it seems that several botanists 

 of eminence have expressed themselves with regard to the 

 preceding facts, in a way that seems to amount, either to a 

 total denial of them, or to a persuasion that they are of too 



* Lind. lntrod. 60, 213. 



