5o6 



SECONDARy CHANGES. 



g In the root the width of the elements first increases, then falls again, and 

 next rises to a constant amount. An increase in length also takes place, but could 

 not be exactly determined. 



The absolute size of the elements is not the same at the same place in 

 different individual trees, but these differences do not infringe the general rule. In 

 order to illustrate the absolute dimensions, some of Sanio's determmations (cf. I.e.), 

 taken from a main axis i lo years old, may here be cited. 



ML. = mean length, MBr. = mean breadth of the tracheides, the latter determined in 



the autumn wood. 



A. Disk 21 years old, from the summit. 



B. 35 » » above the thick branches of the crown. 

 cl ", 72 „ „ from the shaft, 36' above the ground. 

 D. „ 105 „ ., close above the ground. 



The dimensions are expressed in millimetres. 



Annual ring. 



I MBr.: o-oi6; ML.: 0-78 



14 » « » '■?+ 



18 „ „. „ 2.21 



20 „ „ ' „ 2-91 



i> 



21 



0.026 



2-82 



B. 



Annual ring. 



I MBr.: o-oi6; ML.: o-8o 



15 » » » 2'^° 



17 » » >) 2-74 



18 „ „ „ 2-83 



19 » » J) 2-82 



20 „ „ „ 2-82 



22 „ „ „ 2-82 



33 „ 0.028 „, 2-78 



D. 



Annual ring. 

 I MBr.: o.oii ; 



20 I) i> 



29 » » 



30 » » 



31 » I, 

 46 t> » 

 60 „ ,, 

 80 „ „ 



105 



0-028 



ML.: — 



» 1-87 



„ 2.48 



„ 2-6o 



„ 2-65 



„ 2-65 



„ 2-65 



„ 2.6j 



„ 2-63 



In the Dicotyledonous woods investigated ^, the conditions in question vary ac- 

 cording to the species ; some show no increase in the size of the elements in the 

 successive rings : e. g. Mahonia Aquifolium ; or only an inconsiderable one, as in 

 Berberis vulgaris, where only the vessels in the spring wood become wider. 



In the other cases investigated (Caragana arborescens, Sophora japonica, Saro- 

 thamnus scoparius, Acacia longifolia, Carpinus Betulus, Quercus pedunculata, Cornus 

 sanguinea, Rhamnus cathartica, and Ficus elastica), an increase in length takes place 

 from within outwards, which affects the individual forms of tissue unequally. The 



' Sanio, Botaii. Zeitg. 1863, I.e. — Pringsheim's Jahrb. IX. p. 52, &c. 



