Microscopical Essays, 673 



juices cloathing the bubble, gives it form and fubflance. The 

 firfl feafon is the time of it's greatdl ufe, and it immediately after 

 begins to decay. 



The pith has in general been reprefented as much more 

 complex than it really is. It confifts of a range of bladders, 

 lying one over the other. The membrane is fimple, the outline 

 {ingle ; but as it is very difficult to procure it in this fimple fl ate, 

 it is often feen and reprefented under a variety of irregular, 

 though pleafmg forms, which are occafioned by the interfecuoqs 

 of the outlines of the blebs, as feen one over another. 



A duller in any part of the corona, protruding itfelf onward 

 and outward in the growing feafon,* carries a part of the circle 

 out with it. The duller itfelf is a perfect piece of the wood and 

 blea, and the bark which follows it out in it's progrefs per feci ly 

 cl oaths it : thus is the firfl protrufion of the fhoot made, but all 

 this while there is no pith. The continuation of growth is made 

 by the extenfion of all the parts obliquely upwards ; in the courfe 

 of this extenfion they hollow themfelves into a kind of cylinder, 

 of the form of the future branch, and by this difpofition a fmall 

 vacancy is made in their center. This enlarges as they increafe, 

 and as it enlarges it becomes filled with the exudation of thofe 

 little bladders which remain and conflitute the pith, fed from the 

 inner coat of the pith, which already begins to' form itfelf into a 

 new corona. Grew feemed to think, that in fome inllances the 

 pith was of pofterior growth to the other parts, and derived it's 

 origin from the bark ; and that the infertioris of the bark running 



4 N in 



* Hill's Conftrudion of Timber, p. 99. 



