ITS STRUCTURE AND GROWTH. 95 



Sumac, Locust, Honey-Locust (Fig. 1G4), &c. : in these buds the 

 parts are few and very rudimentary, and are mostly formed 

 as they develop. In some, they ai-e naked, that is, are entirely 

 destitute of protecting scales, and exliibit the forming leaves directly 

 exposed to the air, just as they are in herbs. This occurs in many 

 tropical trees, but not in all, and in some shrubs of cold climates, 

 such as our Viburnum nudum and V. lantanoides. But the greater 

 number of plants which have a winter to endure are provided with 

 scaly buds. Those of Beech and Hickory, as well as of Horsechest- 

 nut and Magnolia already referred to, are conspicuous and well- 

 developed examples. The scales serve to protect the tender parts 

 within against injury from moisture and from sudden changes in 

 temperature during the dormant state. To ward off moisture more 

 effectually, they are sometimes coated with a waxy, resinous, or 

 balsamic exudation, as is conspicuous on the scales of the Horse- 

 chestnut, Balsam-Poplar or Balm of Gilead, and Balsam-Fir. To 

 guard against sudden changes of temperature, they are often lined, 

 or the rudimentary leaves within invested with non-conducting 

 down or wool. 



161. The hud-scales themselves are leaves in a modified state. 

 This is evident from their situation and arrangement, which are 

 the same as of the proper leaves of the species, and by the gradual 

 transitions from the former to the latter in many plants. In the 

 turions, or subterranean budding shoots of numerous perennial 

 herbs, and in the unfolding buds of the Lilac and Sweet Buckeye 

 (jEscuIus parviflora), every gradation may be traced between bud- 

 scales and foliage, showing that no absolute line can be di-awn be- 

 tween them, but that the two are essentially of the same nature, i. e. 

 are different modifications of the same organ. 



162. Plan of Vegetation. In fact, a simple stem bears nothing but 

 leaves in some form or other, and its branches are only repetitions 

 of itself, following the same laws. The embryo consists of a pri- 

 mary joint of stem crowned with a bud, the first leaves or leaf of 

 which takes the special form of cotyledons ; the following ones de- 

 velop as ordinary foUage, and leaf after leaf, or pair after pair, is 

 formed and elevated upon the successive intemodes as the stem is 

 built up. At the close of the growing season, if the stem is to 

 endure, this is terminated, as it began, by a bud ; and the bud-scales, 

 if any, are leaves developed in this peculiar form, subservient to 

 protection alone, and borne upon nodes which are never separated 



