TWIGS OF WOODY PLANTS. 3 



than two at a node (sonietiines in Cafall^a). Of the alternate 

 arrangement there are two series, 2-ranked and 5- to 8-ranked. 

 Twigs of the latter series are commonly either 5-ranked or 8- 

 ranked, but in most cases both arrangements may be found in 

 the same species, often on the same individual; and even a 13- 

 ranked arrangement may occur. 



The shape of the leaf-scars is variable, liut varies within fairly 

 well defined limits, so that certain general forms are characteristic 

 of species and often of genera. The catalpa has nearly circular 

 leaf-scars. In the elms, basswood, and in fact most of the 2- 

 ranked genera, the scars are oval or semi-elliptical. The walnuts 

 and hickories have them heart- or shield-shaped. Sometimes the 

 scar becomes narrow and crescent-shaped or U- or V-shaped as 

 in the maples and sycamore. The plums bear oval leaf-scars, 

 while those of the apple are U-shaped. 



The vascular bundles which pass from the stem to the leaf are 

 usually aggregated into definite groups which in the leaf-scar 

 present scars or dots called bundle-scars. The arrangement of 

 these is a character to be noted. 



In plants possessing well-marked stipules these organs leave a 

 scar on the twig at each side of the leaf-scar. Certain genera are 

 characterized by the stipule-scar encircling the twig. Among our 

 trees may be mentioned the magnolias and their relative, the 

 tulip tree ; and the sycamore. The bud scales, being modified 

 stipules, are in pairs encircling the bud. As the bud expands, the 

 scales fall ofi; and leave these scars. The genus Ficiis and some 

 other exotics also have encii"cling stipule-scars. Occasionally the 

 stipules are transformed into spines as in the black locust and 

 some other woody Leguminosae. In prickly ash similar spines 

 occur in pairs at the nodes but they are not transformed stipules. 

 Prickles may be aggregated at the nodes to simulate stipules as 

 the triple prickles of certain gooseberries. 



Buds. — These may be lateral or terminal. The former occur 

 in the axils of the leaves ; the latter at the end of the stem. In 

 the ordinary course of development the buds expand in the spring 

 and the growth in length of the twigs takes place rapidly during 

 the time that the leaves are attainins: their full growth. The 



