58 



MORPHOLOGY OF STEMS. 



portions die and decay as corresponding additions are made to 

 the opposite growing extremity. Each year's growth is often 



marked conspicuously, sometimes by a strong contraction where 

 the interruption took place, as in certain species of Iris (Fig. 216) ; 



or by the circular im- 

 pressed scar (likened to 

 the impression of a seal) 

 in Solomon's Seal ; this 

 being the place where 

 the annual aerial stem, 

 bearing the vegetation, 

 separated in autumn 

 from the perennial rhi- 

 zoma. The numerous 

 slender lines encircling the rootstock are the scars left after the 

 decay of the scale-like leaves or bud-scales, such as are seen at 

 the young and growing end of the rootstock. 

 The rootstock of Diphylleia, of the Alleghanj^ 

 Mountains (Fig. 101), is similar; but the 

 yearly growths are so exceedingly short that 

 they become vertical, the bud of each j-ear 

 is close to the stalk of the year preceding, 

 and the scars marking previous growths are 

 in contact. 1 Trillium makes a short and 

 mostly vertical rootstock, which, when it 

 remains simple and dies away promptly 

 below (as in Fig. 102), comes nearly within 

 102 V>"! the definition of a corm. But in several 



1 The rootstock in Polygonatum and Diphylleia is a sympodium (110, note), 

 the terminal bud developing yearly the growth above ground and perishing 



FIG. 100. Rootstock of Polygonatum or Solomon's Seal, with the terminal bud, the 

 base of the stalk of the season, and three scars from which the latter has separated in 

 as many former years. 



FIG. 101. Rhizoma of Diphylleia cymosa, showing six years' growth, and a bud for 

 the seventh : a, the bud : ft, base of the stalk of the current year : c, scar left by the 

 decay of the annual stalk of the year before; and beyond are the scars of previous years. 



FIG. 102. Shoot and young rootstock of Trillium erectum, with only terminal bud. 



