410 



Mil. MAIN S VEGETABLE PHYSIOLOGY. 



and the wood of one of four years' growth. But this difficulty is not greater, 

 indeed not -quite so incomprehensible, as is the other supposition already alluded 

 to, namely, that all increments are elaborated from juices and qualities inherent in 

 the plant, or formed by accidental associations of certain electro-chemical bodies 

 extractable from the earth, air, and water. The identity of the vital envelope, 

 during summer, is visible and palpable ; and if in winter it be only a cincture of 

 transparent cellular matter, no doubt need be entertained of its subsequent expan- 

 sibility. That vegetable matter appears in the first stage of its existence as a 

 colourless homogenous mass is indisputable ; and that it gradually gains consistency 

 and organic form, may be easily believed by examining an orange when first visible 

 in the flower, and again when fully ripe and deprived of its juice. Besides, the 

 accrescent powers and indefinite limits of vegetation in this case, should banish 

 incredulity ; in many other instances it is equally surprising ; witness the mon- 

 strous gourd, the majestic oak, the magnificent Banyan Fig; the latter shading 

 acres of surface, all originating in an atom of a seed. 



" The new layer of wood which is added on the old stem or trunk, ranges with 

 the first layer of wood on the terminal shoots. On the latter all primary buds, 

 and consequently branches, originate. The shoots developed this year, except 

 water shoots *, are based on the alburnum formed on the last ; and the buds formed 

 in this year are seated on this year's alburnum, and on which they remain to be 

 developed in the next or some following year. The pith, wood, buds, and bark of 

 every shoot are all simultaneously produced. 



" But all buds or branches are not primary. Such as are produced from an old 

 stem (6, Fig. 47) whether naturally, or by consequence of pruning, may be called, 



Example of a primary shoot a, and a secondary shoot b. The former is seated on the 

 alburnum of the first year, the latter on that of the third. 



for the sake of distinction, secondary^. These can have no immediate connection 

 with the first formed layer of wood and pith, and therefore invariably spring from 

 the envelope. The following delineation represents the disposition of the layers of 

 wood and bark, with the places of the primary and secondary buds or shoots, on a 

 section of an abbreviated stem of a tree of three years' growth. 



* Water shoots are such as are produced on luxuriant growing shoots of the 

 present year, frequently seen on the peach, apricot, and always on the grape vine. 



f Botanists suppose that there are what they call " adventitious buds," that is, 

 if buds come forth from other places than the axils of the leaves or bractea, they 

 are adventitious and new creations. Their appearance, indeed, may be adventi- 

 tious, but not their identity. If a bud can be produced without a rudiment, so may 

 a whole plant. 



