GENERAL MOEPHOLOGY OF THE PLANT 39 



perennial. They are annual when they live only through 

 one season, that is, between the spring and winter ; biennial, 

 when they spring from seed in one season, and die in the 

 second, after producing flowers, fruit, and seed; awA. perenoiial, 

 when they spring from seed in one season, and continue to live 

 through a succession of years, the sub-aerial parts dying down 

 in the autumn, and in the succeeding spring again coming up as 

 herbaceous stems. The term tree is apphed if the branches 

 are perennial and arise from a trunk. "When the branches are 

 perennial and proceed directly from, or near to, the surface of 

 the groamd, without any trunk, or where this is very short, a alirub 

 is formed ; this, when low and branched very much at the base, 

 is denominated a hush. The term undershruh is applied to a 

 small shrub which is intermediate in its characters between an 

 ordinary shrub and an herb ; in such a plant some of its branches 

 generally perish annually, while others are more or less permanent. 

 All these 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 branches from its side, as in most 

 Firs ; such a stem has been termed excurrent. When the main 

 stem is arrested in its growth by the process of flowering, or 

 some other cause, and the lateral buds become the more 

 vigorously developed, so that the stem appears to divide into a 

 number of irregular branches, it is said to be deliquescent. 

 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 ; while 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. If the branches are firm, and spring at an acute angle 

 from 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, 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 pendulous. In some 

 cases this weeping appearance arises from the weakness and 

 flexibility of the branches, as in the Weeping Willow and Weep- 

 ing Birch. The relative length also of the upper and lower 

 branches gives rise to corresponding differences in the general 



