36 



THE STEM, OR ASCENDING AXIS. 



beecli, biicb, oak, and especially in the spruce — trees with oval or pyramidal 

 crowns. 



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

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

 ditferent degrees of divergeucy, 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 foem OF the teunk sometimes changes with age, especially in tropic.il 

 reo-ions, some distorted by huge local excrescences, others swelling out ni tho mid^i 

 to " aldermanic" proportions. 



47. tf, An «1*1 willow (Salix Babylonica") with gnarled .and misshapen trunk, h, Caudex of a 

 cactufi (Echinncactns Ottonis). c, Eonibax, of Brazilian forests, with disteniled trunk, d. Pal- 

 metto (Babal, Adns), the caudex rough with the persistent bases of the petioles. -^ 



17S. C-A-UDEr is a term now apphed to the peculiar trunk of the palms and tree- 

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

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

 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 fuU 

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

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

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

 springs dry up under the torrid sun. 



178. 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 convc- 

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



