CLASSIFICATION OF STEMS. 



75 



or shortness of which fall within certain 



fairly defined and restricted limits; the 



latter, those which either possess an in- 

 definite extension, or the definite length 



of which is a great many times their 

 thickness. Terms indicative of their form 

 and consistency do not differ materially 

 from those applied to other stems and 

 roots. They are almost always sympo- 

 dial. They are very subject to flattening, 

 the flattened surfaces usually looking up- 

 ward and downward. The presence or 

 absence of branches is always character- 

 istic. The manner in which the roots take 

 their origin is equally so. These may 

 form a circle (Fig. 368) or be restricted to 

 the under surface (Fig. 369). The num- 

 ber of roots developing from a node is 

 usually fairly characteristic. So is the 

 persistency or brittleness of these, and the 



fined to the upper surface. If the latter, 

 the scar may be of characteristic form, 

 as linear, elliptical, circular, cordate, cres- 

 cent shaped or V-shaped (Fig. 373a). 

 Finally we note that annular or longitu- 

 dinal folds, thickenings, wrinkles or con- 

 strictions are characteristic of certain rhi- 

 zomes as well as of roots, particularly in 

 the dried state. 



As to their mode of extension, stems 

 may be Simple, or Branched. A stem de- 

 nominated as simple is not necessarily en- 

 tirely destitute of branches, as floral 

 branches or small branches near the sum- 

 mit are permitted. It has already been 

 shown that stems may develop monopodi- 

 ally or sympodially. The stem of a tree, 

 which continues, except in case of acci- 

 dent, to develop monopodially, is called 

 Excurrent. One which after a time loses 



F. 



g'^13 



characters of the stumps or scars which its main stem in a number of branches, as 

 they leave, as well as their form, which is for instance the elm, is Deliquescent 

 very often triangular or quadrangular in 

 section. Their structure, as observed 

 either with the lens or with the micro- 

 scope, is characteristic and of diagnostic 

 value. Sometimes the roots are not only 

 restricted to a certain portion of the node, 

 but in the case of short rhizomes are re- 

 stricted to a definite portion of the latter 

 (Fig. 370). The relative length of the 

 nodes of a rhizome calls for close atten- 

 tion, as compared with its diameter or 

 thickness, and so does the absolute or 

 measured length. The relations of the 

 erect portions of the rhizome to the hori- 

 zontal and the stumps or scars left by the 

 former upon their death or separation 

 constitute one of their most important 

 diagnostic characteristics. Commonly 

 disarticulation occurs with the produc- 

 tion of a cup-shaped scar. This scar will 



r,g.373A 



Fig'.3T3B 



Kj,^"J> ^- 



Sympodial stems possess several well- 

 marked classes. If extension is by means 

 of a pair of branches at the summit, these 

 and their branches successively forking 

 in a similar manner (Fig. 373A), the 

 growth is Dichotomous or Bifurcating. 

 (Jf IS fn bp imtpd that these two terms are 



be characteristic as to whether it form a applied in a restricted sense to the form of 

 depression in the general surface (Fig. dichotomy which is produced by the ver- 

 371) or be elevated upon a base (Fig. 372), 

 as will the length of the latter, the form 

 and depth of the scar and the characters 

 of its edge. The size of the scar, that is 



tical division of an apical cell, so that the 

 form figured in 373A is by some authors 

 denominated "Falsely Dichotomous."). 

 If but one branch develop from a node, 



its lateral breadth as compared with the the resulting sympodium may be of either 



thickness of the internode, is also note- of two classes, according to whether the 



worthy. Leaf scars, or leaf remains, upon successively developing branches are all 



rhizomes, call for the same examination developed upon one side of the axis (Fig. 



as do the stem scars. They may surround 373b), or produce the same effect by as- 



the entire rhizome, in which case they are suming such a uniform direction, in either 



designated Annular, or they may be con- of which cases we get the Secund form, 



