102 OBGANOGBAPHY. 



applied if the branches are perennial and arise from a trunk ; 

 and the collection of branches which thus arise from the trunk 

 and form the head of a tree is called a coma. When the 

 branches are perennial and proceed directly from, or near to the 

 surface of the ground, without any trunk, or where this is very 

 short, a shrub is formed ; this when low and branched very much 

 at the base, is denominated a bush. The term undershrub is 

 also applied to a small shrub which is intermediate in its cha- 

 racters between an ordinary shrub and an herb, thus, when 

 some of its branches generally perish annually, while others 

 are more or less permanent. All the above kinds of stems 

 are connected by intermediate links, so that in many cases they 

 are by no means well defined. 



If the terminal bud of a stem is continually developed, the 

 axis upon which it is placed is prolonged upwards from the 

 earth to its summit, giving off from its side the lateral branches, 

 as in most Firs ; such a stem has been termed excurrent. 

 When the main stem is arrested in its development by the 

 process of flowering, or some other cause, and the lateral buds 

 become the more vigorously developed, so that the stem ap- 

 pears to divide into a number of irregular branches, it is said 

 to be diliquescent. These different kinds of growth influence 

 materially the general form of trees. Thus, those with excurrent 

 stems are usually more or less conical or pyramidal. Those 

 with deliquescent stems are rounded or spreading. The general 

 appearance of trees also depends upon the nature of the lateral 

 branches, and upon the angle which they make with the stem 

 from which they arise. Thus, if the branches are firm, and arise 

 at an acute angle to the stem, as in the Cypress and Lombardy 

 Poplar, they are erect, and the tree is more or less narrowed ; 

 if they come off at a right angle, the branches are spreading or 

 fatent, as in the Oak and Cedar ; if the angle is very obtuse, or 

 if the branches bend downwards from their origin, as in the 

 Weeping Ash and Weeping Elm, they are termed weeping or 

 fendulotis ; in other cases this weeping appearance arises from 

 the weakness and flexibility of the branches, as in the Weeping 

 Willow and Weeping Birch. The relative length also of the 

 upper and lower branches will give rise to corresponding differ- 

 ences in the general appearance of trees. Thus, if the lower 

 branches are the longest and become shorter as they approach 

 the top, the whole will be shaped like a cone or pyramid, as in 

 the Spruce Fir ; if the middle branches are longer than those of 

 the base and apex, the general appearance will be rounded or 

 oval, as in the Horsechestnut ; if those of the top are the most 

 developed, the form will be umbrella-like, as in the Italian Pine. 



Besides the forms of stems and branches already described, 

 there are some others which have received special names. These 

 are the Sjpine and Tendril. 



