36 



THE STEM, OR ASCENDING AXIS. 



beech, birch, oak, and especially in the spruce — trees with oval or pyramidal 

 crowns. 



174 But in the other, the solvent axis, as seen in the elm, the apple-tree, 

 the trunk suddenly divides into several subequal branches, which thence depart with 

 different degrees of divergency, giving the urn form to the elm, the rounded form 

 to the apple-tree, the depressed form to the sloe-tree (Viburnum) and dogwood. 



175. The form op the trunk sometimes changes with age, especially in tropical 

 regions, some distorted by huge local excrescences, othera swelling out in the midst 

 to " aldermanic" proportions. 



4T. a, An »ld willow (Salix Babylonica) with gnarled and misshapen trunk, b, Catnlese of a 

 cactus (Echinocactus Ottonis). c, Bombax, of Brazilian forests, with distended trunk, d, Pal- 

 metto (Sabal, Adns), the caudex rough with the persistent bases of the petioles. 



176. Caudex is a term now applied to the peculiar trunk of the palms and tree- 

 ferns, simple, branchless columns, or rarely dividing in advanced age. It is pro- 

 duced by the growth of the terminal bud alone, and its sides are marked by tho 

 scars of the fallen leaf-stalks of former years, or are yet covered by their persistent 

 bases. 



177. The stock or caudex of the cactus tribe is extraordinary in form and sub- 

 stance. It is often jointed, prismatic, branched, always greenish, fleshy, and full 

 of a watery juice. Instead of leaves, its lateral buds develop spines only, the stem 

 itself performing the functions of leaves. These plants abound in tho warm regions 

 of tropical America, and afford a cooling, acid beverage to the thirsty traveler when 

 springs dry up under the torrid sun. 



1"78. The- vine is either herbaceous or woody. It is a stem too slen- 

 der and weak to stand erect, but trails along the ground or any conve- 

 nient support. Sometimes, by means of special organs for this purpose, 



