THE HIGHER CRYPTOGAMIA. 361 



the entire suppression of intercalary cell-multiplication in 

 the joints of the principal axis, leads necessarily to the result 

 that the younger portion of the bark formed out of the con- 

 fluent basal portions of the leaves projects far beyond the 

 punctum vegetationis of the principal axis. The top of old 

 plants exhibits a remarkable funnel-shaped depression, upon 

 whose inwardly-inclined slope the younger leaves which 

 sheath one another are seated (PI. LI, fig. 1; PL LII, fig. 1). 

 The terminal bud occupies the base of the crateriform de- 

 pression, exhibiting a blunt cone of cellular tissue (PI. L, 

 figs. 1,2), surrounded at moderate distances by the rudi- 

 ments of the youngest leaves, which in plants of from five to 

 eight years old have the T 5 3 arrangement. 



The nature of the cell- multiplication of the terminal bud 

 remains (as has been said) the same throughout the entire 

 life of the plant. The alternately oblique septa by which 

 the apical cell divides in repeated succession, are inclined to 

 the large lobes of the bark ; a plane passing through the 

 furrow of the stem cuts those septa at right angles. The 

 daughter-cells of the cells of the second degree soon divide 

 by transverse septa, and become cells of the third or fourth 

 degree (PI. LI, figs. 1, 2). Close under the apex of the termi- 

 nal bud the arrangement of the cells, which at first was 

 ladder-like, is changed into a concentrical scale-like arrange- 

 ment. The inner cells — those nearest to the axis of the 

 stem — of the derivatives of the third- and fourth-youngest 

 cell of the second degree, expand remarkably in width in a 

 direction radial to the longitudinal axis of the wood. By 

 this means the terminal bud, even above the place of origin 

 of the youngest leaf, is quite flattened (PI. L, figs. 1, 2). 



The effect of the yearly renovation of the cambial layer is 

 not only to increase and renew the cortical tissue, but new 

 spiral cells also become added, although only sparingly, to 

 the wood of old vigorous plants. Individual cells of the 

 cambium, separated by two or three cambial cells from the 

 older principal mass of the wood, often exhibit thickenings 

 of the walls, which by their delicacy and want of colour 

 betray their undoubtedly recent origin (PI. LI, fig. 2). 

 New elementary organs are never added to the oldest por- 

 tions of the wood, those namely which are formed in the one 



