STEMS OF DICOTYLLUONS 



159 



In this way we see that the increase of dicotyl trunks 

 and branches is approximately in an elongated cone (Fig. 



306), the number of 

 rings gradually diminish- 

 ing toward the top till at 

 the terminal bud of each 

 bough it is reduced to 



fed 



305. — Diagrammatic view of a leafy stem 

 of clematis, showing the arrangement of the 

 fibrovascular bundles : a, b, c, ~e,f, d, the 

 fascicles from the lower pair of leaves; i,^, 

 I, — k, h, m, the fascicles from the second 

 pair of leaves ; ^, r, s, — />, n, o, the fascicles 

 from the third pair of leaves ; x, t, fascicles 

 of the fourth pair of leaves ; ;3. a, —7, S, pairs 

 of undeveloped leaves not as yet having 

 fascicles (Gray, after N AGELl) . 



306. — Diagram illustrating the an- 

 nual growth of dicotyledons. 



a single one, as in the 

 stems of annuals. 



Sometimes a late au- 

 tumn, succeeding a very 

 dry summer, will cause trees to take on a second growth, 

 and thus form two layers of wood in a single season, so 

 we can not always rely absolutely upon the number of 

 rings in estimating the age of a tree. 



225. The Stems of Conifers. — Examine a young stem 

 of pine, and compare with the one just studied. What 

 difference do you notice .-" This absence of the duct pores 

 constitutes one of the most conspicuous differences be- 

 tween the stems of conifers (cone bearers) and dicotyledons. 



