STEMS BEARING FOLIAGE-LEAVES 



657 



whilst within masses of wood are continually formed and are deposited on the 

 bundles of woody cells and vessels produced in the first year thus increasing the 

 circumference of the stem. Such a stem is said to be "woody" (stirps lignea). 

 Woody stems which have been thickened continuously in this manner for centuries 

 sometimes attain a circumference of 50 metres; that of the Mexican conifer 



Fig. 153. Agaves of the Mexican uplands (from a photograph). 



(Taxodium mucronatum) has even been found with a girth of 5T88 metres; this 

 circumference exceeds that of the above-mentioned stem of Centunculus more than 

 a hundred thousand times. The thickness of the stem is in general greatest at the 

 base and gradually tapers off above; only a few palms are thicker immediately 

 below their crown of green leaves than at the base, and in the strange cotton-trees 

 of the Brazilian catingas (Cavanillesia tuberculata) of which an illustration is 

 inserted opposite, the stem forms a swollen, barrel-shaped mass attaining its maxi- 



VOL. I. *2 



