34 MORPHOLOGY, OE COMPARATIVE ANATOMY. 



Woody Stem. Buds. The stem characteristic of arborescent 

 plants presents, itself in two principal classes of form : one, 

 where it is branched, constituting a trunk (truncus) ; the other, 

 where it is an unbranched column, bearing its foliage as a terminal 

 crown, forming what is sometimes called a stoclc (caudex). 



These differences depend upon the number, position, and mode of 

 development of the buds, only a few of which, in most cases, lengthen 

 into shoots, the others becoming 1 arrested in their growth. When, as in 

 Dicotyledonous trees generally, axillary buds, or those formed on the side 

 of the stem in the axils, or point of junction of the leaf with the stem, 

 are developed into branches, we find a ramified trunk j when the terminal 

 bud alone unfolds, as in most Palms, the globular and columnar Cactacese, 

 and the Cycadacere, a simple columnar caudex is formed. 



It is evident from this, that the mode of branching of a stem must 

 be essentially dependent on the arrangement of leaves ; but a com- 

 plication arises from the frequent suppression or non-development of 

 the axillary buds, often according to a regular plan ; and, in fact, it 

 is very seldom that all the axillary buds of a stem are developed (figs. 

 27 & 28). 



Fig. 27. Fig. 28. 



Fig. 27. Plan of indefinite ramification, with development of terminal and axillary shoots. 

 Fig. 28. Plan of definite ramification, with arrest of the terminal and development of the 

 axillary buds, producing bifurcation. 



This abortion of axillary buds is most extensively displayed in Mono- 

 cotyledons .; for the frequent existence of dormant buds in the leaf-axils, 

 even of Palms, is shown not only by the occasional production of isolated 

 lateral shoots, but by the frequent, and in some cases constant, development 

 of buds in the axils of the basilar leaves, forming suckers round the base of 

 the stem. A similar phenomenon occurs in the propagation of bulbs, &c. 



Among Dicotyledonous plants, the influence of the suppression of buds 

 in regular order is very great. In the Labiatee we have opposite leaves ; 

 and as pairs of axillary buds are developed, the ramification is generally 

 very symmetrical ; in some of the CaryopkyUacea with similarly decussate 

 opposite leaves, one axillary bud only is developed, and the other is sup- 

 pressed at each node, so that the branches, arising one by one, stand 

 spirally arranged upon the stem. In the Firs, the branches often appear 

 to arise in whorls, owing to the periodical development of a number of buds 

 in the axils of closely succeeding spirally arranged leaves, with leng 

 intervals of total abortion. 



