FOEMS OF STEMS. 45 



in one or several rows, forming simple filaments, as in Confervae ; or 

 branched and interlaced filaments, as in some Fungi ; or cellular 

 expansions, as in Lichens and sea-weeds. 



Stems have usually considerable firmness and solidity, but some- 

 times they are weak, and either lie prostrate on the ground, thus 

 becoming procumbent ; or climb on plants and rocks by means of 

 rootlets like the Ivy, being then called scandent ; or twist round other 

 pla,nts in a spiral manner like Woodbine, becoming voluUle. Twining 

 plants turn either from right to left, as the French bean, Convolvulus, 

 Passionflower, and Dodder, Periploca, and Gourd ; or from left to right 

 (left-handed screw), as Honeysuckle, Twining Polygonum, Hop, and 

 Tamus. Bryony tendrils twine from right to left, and left to right, 

 alternately. In warm climates twining plants {lianas) often form 

 thick woody stems ; while in temperate regions they are generally 

 herbaceous. Exceptions, however, occur in the case of the Clematis, 

 Honeysuckle, and Vine ; the twining stem of the vine has been 

 called sarmentum {sarmentwm, a twig, or cutting of a vine). Some 

 stems are developed more in diameter than in height, and present a 

 peculiar shortened and thickened aspect, as Testudinaria or Tortoise- 

 plant, Cyclamen, Melocactus, Echinocactus, and other Cactacese. 



Stems have a provision for a symmetrical arrangement of leaves 

 and branches, — nodei (nodus, a knot), or points whence leaf-buds are 

 produced, being placed at regular intervals. No such provision occurs 

 in roots, which ramify irregularly, according to the nature of the soil. 

 The intervals between nodes are called internodes. The mode in which 

 branches come off from the nodes gives rise to various forms of trees, 

 such as pyramidal, spreading, or weeping ; the angles formed with 

 the stem being more or less acute or oblique. In the Italian Poplar 

 and Cypress the branches are erect, forming acute angles with the 

 upper part of the stem ; in the Oak and Cedar they are spreading or 

 patent, forming nearly a right angle ; in the weeping Ash and Elm 

 they come off at an oblique angle ; while in the weeping Willow and 

 Birch they are pendulous from their flexibility. The comparative 

 length of the upper and under branches also gives rise to differences 

 in the contour of trees, as seen in the conical form of Spruce, and the 

 umbrella-like form of the Italian Pine (Pinus Pinea). The branching 

 of some trees is very peculiar. In the Amazon district many Myris- ' 

 ticacese and Monimiaceee have verticillate branches coming off in fives. 

 Some Amazon trees taper remarkably downwards, so as to have a form 

 like an inverted cone or pyramid. This is seen in the Mulatto tree 

 (Eukylista Spruceana), one of the Oinchonacese. 



The buds of trees are developed in different ways. In some, such 

 as the Oak and Birch, the terminal bud of each shoot produces 

 yearly a new portion of the shootj while the flowers come off from 

 axillary buds. Again, in other trees, as LUac and Horse-chestnut, the 



