36 



MOEPHOLOGY, OK COMPARATIVE ANATOMY. 



Fig. 32. 



elongated, and the lateral ramifications are numerous, the result is 

 a shrubby plant ; if the growth of the main trunk predominates for 

 a long time, but ultimately slackens, and the side branches grow 

 more, the form seen in ordinary trees appears, where the top of the 

 tree is more or less globose, as in what are called " round-headed " 

 trees, like the elm : while if the growth of the central stem by the 

 terminal bud is predominant throughout life, we have tall straight 

 trunks with comparatively small ascending branches, such as are 

 seen in the Lombardy Poplar, which is an instance of afastiyiate tree. 



The originally cylindrical form of trunks often undergoes considerable 

 alteration with age, depending upon 

 peculiar modes of development of 

 the woody structure within. Irre- 

 gular prominences occur commonly 

 on such old timber-trees as have 

 large branches, greater enlargement 

 taking place in the line between 

 the base of the branches and the 

 roots ; this is often seen on old 

 Oaks. Some tropical trees produce 

 vast buttress-like projections in the 

 same way. The forms of the trunk 

 of the woody climbing plants of 

 tropical forests present very remark- 

 able irregularities, arising either 

 from a twining habit, or from ir- 

 regular development caused from 

 lateral pressure or otherwise. In 

 some kinds of Bomlax (fig. 32), 

 and in Delabechea (Bombaceae), the 

 trunk is swollen out in the shape 

 of a great flask between the root 

 and the main branches. 



The Stock or caudex is an undivided woody trunk, produced by 

 the annual unfolding of a single terminal bud. Its interuodes are 

 commonly little developed, so that its sides are marked with the 

 scars of its fallen leaves ; sometimes, however, the interuodes are 

 developed, and then the stock has a jointed appearance, from scars 

 or actual articulations at the nodes. The stocks of the Cactacea3 

 are remarkable for their form and consistence (figs. 35-37); their 

 lateral buds are developed into tufts of spines, svhich are the repre- 

 sentatives of the leaves of undeveloped branches. 



The stock of the Palms exhibits considerable variety of form. In the 

 Cocoanut- ( Coco* ) and Date-palms the internodes are scarcely developed, 

 and the scars of the leaf-stalks, arranged in spiral order, cover the sides. 

 The same holds good of the stock of (Jycas and its allies, of Xanthorrhcea, 

 and other arborescent Monocotyledons, and also of the stock of the Tree- 



Trunk of a Brazilian Bombax. 



