144 LETTER X. 



Dicotyledonous plants, a subject upon which I as yet 

 have said almost nothing. Get a branch of Hazel, 

 Beech or Oak, and divide it horizontally, so as to 

 have a view of the whole of the inside from one side 

 to the other, the section forming a circle which is 

 bounded by the bark. Let the section be rendered 

 smooth by a sharp knife or a plane, so that all the 

 parts may be distinctly seen ; you will then remark 

 in the centre a pale roundish spot, which a glass will 

 shew to be formed of a soft spongy substance : it is 

 the PITH, a cellular provision of nature for the support 

 of the young buds when they are too weak to obtain 

 food from more distant sources. Next the pith follow 

 several rings of wood, each of which is composed of 

 an infinite number of tubes, and was the produce of 

 one year's growth, so that the number of the rings 

 tells you the number of years the branch has been in 

 acquiring its present size ; the most external of the 

 rings is the youngest, and also the palest, while the 

 most internal or the oldest is of a deep brown colour ; 

 the pale is called the sapwood, the brown the heart- 

 wood ; the latter, which is much more durable than 

 the former, is filled with a substance of a hardening 

 nature, which was originally formed in the leaves, 

 and which is stored up by Providence in the centre of 

 the stem, where it lies beyond the reach of accident 

 or injury, until old age comes and produces decay ; 

 originally the heartwood was sapwood, and that 

 which is sapwood now, would have become heart- 

 wood in a few years, if you had not cut off the 

 branch. It is in the sapwood chiefly that the vital 



