The Structure of Stems 



141 



tiureaii of A.griciUlure, P. I 



Fig. 82. Stripping abaca for fiber. The long petioles are pulled under toothed knives 

 which scrape the soft tissues from the bundles. Abaca is a monocot, and the fiber is com- 

 posed of an entire bundle. 



thus form a hard layer beneath the epidermis (Fig. 79). Some 

 monocot stems, hke the palms and dragon tree, increase in thick- 

 ness a number of years during their early life. This is accom- 

 plished by the development of secondary cambiums in the pith 

 between the bundles. The cells of the secondary cambiums 

 divide, forming new bundles between the older ones. In this way 

 the stems increase in diameter, without forming annual rings. 



Dicot stems are enlarged by the development of new layers of 

 cells between the wood and the food-conducting tissue. It follows 

 that there will be annual rings in such stems. 



The structure of conifer stems. The conifers, like the dicots, 

 have their bundles arranged in a cylinder. In structure these 

 bundles are somewhat similar to those of dicots, except that the 

 wood and water-conducting tissues are not distinct. The wood 

 cells form the water-conducting tissue as well as the mechanical 

 tissue. In keeping with their double function, these cells (tra- 



