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 51*88 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 tuherculata) of M'hich an illustration is 

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



