SECT. VI. THE CAUDEX. 



Hemlock (PI. VIII. Fig. 14.), which constitutes 

 externally a fluted column, is taken and divided 

 by a transverse section, it will be found to consist 

 of an epidermis containing a hollow cylinder of 

 united pulp and fibre, lined with a soft and spongy 

 pith, which is itself tubular ; and again lined with 

 a fine and transparent membrane, consisting of a 

 most intricate plexus of soft and delicate fibres, 

 forming an ultimate cavity, which is sometimes 

 partly filled up with a fine and cottony down, or 

 with fine and transverse diaphragms resembling 

 cobwebs. 



But the circular row of bundles observable in 

 the above plants, and others of a similar structure, 

 is not the same in all. Sometimes it is simple, as 

 in Hemlock ; and sometimes it is compound, as in 

 the Parsnep. In the former case it consists merely 

 of a succession of individual bundles distributed in 

 a circular row, so as to complete the cylinder. In 

 the latter it consists of a succession of individual 

 bundles, traversing the pulp in a direction from 

 the circumference to the centre, as far as the pulp 

 extends, and then returning from the centre to 

 the circumference, after forming a fold, and so on 

 till the cylinder is completed by a succession of 

 folds. 



It should be also added that the tubular stem 

 does not always form one continued cylinder, ex- 

 cept in some of the Agarics, but rather a succession 

 of individual cylinders united to one another by 



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