TWIGS 9 



Studies of the pith may be facilitated by application of a small 

 drop of phloroglucin, followed by a drop of hydrochloric acid. This 

 results in the wood turning a bright red in color, presenting the 

 outline of the pith in sharp focus. 



Lenticels. Lenticels are small, often wart-like prominences 

 scattered over the surface of twigs; they serve to admit air to the 

 living tissues beneath (Figs. 6, 7). They may be circular in shape 

 or quite irregular. In cherries and birches they are elongated hori- 

 zontally. In some cases they are relatively conspicuous, as in 

 elder, in other cases quite inconspicuous. In general they are of 

 little value in identification of twigs. 



Spur Shoots . In some species (e.g. , larch, birch) certain 

 twigs grow very slowly and appear as dwarf branches, even though 

 they may bear a normal number of leaves. A spur shoot is short, 

 usually stocky, and with crowded leaf scars. Often the flower buds 

 may be produced on spurs, as in apple and pear (Fig, 14). 



Prickles and thorns. Small spines or prickles occur on the 

 twigs of numerous species of woody plants and they are often diag- 

 nostic in character. In some cases they represent modified leaves, 

 as in barberry. In other cases they are modified stipules, as in 

 black locust (Fig, 17), while in still other cases they are cortical 

 emergences (outgrowths of the cortex), scattered over the surface 

 of the twig, as in rose and gooseberry. 



Thorns, on the other hand, are modified sharp-pointed twigs, 

 and have the vascular bundles characteristic of other twigs. In 

 some cases careful examination will reveal the presence of tiny 

 buds and leaf scars. They may be branched, as in honey-locust, or 

 unbranched, as in hawthorn. In some instances (e.g., crabapple), 

 a twig may be sharp-pointed, without actually appearing to be a 

 thorn and might represent a structure from the evolutionary stand- 

 point on the way to becoming a thorn. 



FRUITS AND FLOWERS 



Fruits. A true fruit is a ripened ovary, bearing one or more 

 ripened ovules, the seeds . The wall of the fruit, developed from 

 the wall of the ovary, is called the pericarp. This pericarp may 

 be fleshy, relatively soft and juicy, or dry , relatively hard and 

 tough; of course all sorts of gradations exist between these two types, 



Fruits are quite often present on woody plants in winter. 

 These are most likely to be dry fruits, since fleshy fruits are 

 more perishable and are likely to have fallen and rotted, or to have 

 been eaten by animals, particularly birds. Those fleshy fruits 

 which do persist until winter are likely to have withered, as the 

 coralberry, or to be fruits with scanty pulp, as the hackberry. 



