108 BOTANY. [CHAP. in. 



rigid, erect, woody trunk, an ancient type of which is 

 shown at fig. 25. This plan of structure, with various 

 modifications as it passed through Monocotyledons with 

 the single terminal bud, to the dicotyledonous plan of 

 breaking up into numerous branches and bearing an 

 indefinite number of buds, is even at the present day 

 most general, and certainly such a framework as seen in 

 the oak or the beech is a very effectual arrangement for 

 defying the elements under ordinary circumstances. In 

 the mode of arrangement of the branches there is a 

 gradual evolution or improvement observable, that is 

 most to the purpose that of equally exposing all the 

 leaves to light in the latest phase of plant development, 

 the dicotyledonous group. In the Gymnosperms, the 

 usual arrangement of the branches is in whorls or 

 verticils produced at intervals on the stem; these whorls 

 of branches grow out at right angles to the stem, and the 

 secondary branches all grow in the same plane forming 

 tier above tier, each one overshadowed by the tier above, 

 and consequently only receiving a comparatively small 

 amount of light as compared with the typical dicotyle- 

 donous arrangement as illustrated by the ash or the oak, 

 where the numerous primary branches start from the top 

 of the trunk and spread in every direction, the youngest 

 portions that bear the leaves being always produced at 

 the circumference of the head, consequently the great 

 bulk of the leaves are produced at the circumference 

 where they are fully exposed to light. In spite of the 

 many modifications and improvements, external and 

 internal, already indicated, the massive trunk idea 

 must be considered as a failure, its advantages being 

 neutralized by its extreme cost to the plant, for it must 



