46 ON STEMS. 



turn escapes from bondage, but, rising vertically, it en- 

 closes and confines the first layer. 



Caroline. The second layer from the prisoner becomes 

 the gaolar ; but its prisoner does not excite my commis- 

 eration, for the first layer, having learnt how to escape, 

 doubtless profits by its experience, and rises above the 

 fetters with which it is encircled. 



Mrs. B. Yes ; the first layer thus makes a shoot up- 

 wards every year, and the new layers follow its course in 

 regular succession. This mode of growing, you must 

 observe, renders the form of the stem conical, the num- 

 ber of layers diminishing as the stem rises. 



These layers of wood attain a state of maturity, when 

 they become so hard by continued pressure as to be no 

 longer susceptible of yielding to it. Previous to this pe- 

 riod, the layers bear the name of alburnum, signifying 

 white wood, for wood is always white until it reaches this 

 degree of consistence. The length of time requisite to 

 attain a state of maturity varies extremely, according to 

 * the nature of the wood. In some trees five years are 

 sufficient for this purpose ; in others ten or twenty are 

 necessary ; and the Phyllyrea requires no less a term 

 than fifty years to convert its alburnum into perfect wood. 

 When once the first layer has attained this point of ma- 

 turity, the others naturally follow in succession, accord- 

 ing to their respective ages. 



Emily. But are those dark-colored woods, such as 

 mahogany and rose-wood, ever white ? 



Mrs. B. Yes ; and what is still more remarkable, 

 ebony, a wood which is completely black, is white until 

 it has attained this state of maturity. Here is a small 

 piece of a branch of ebony cut transversely : you see that 

 the interior parts are perfectly black, and are surrounded 

 by a ring of white wood or alburnum. The difference 

 between the alburnum and perfect wood is less marked 



220. What comparison does Caroline make to illustrate the relation 

 of the different layers of wood to each other! 221. What renders the 

 form of the stem conical! 222. When do layers of wood attain a 

 state of maturity! 223. By what name are they previously called, 

 and what the propriety of this name! 224. What length of time with 

 different trees is required to attain maturity! 225. Are dark colored 

 woods ever white ; and what ones are! 226. What is the appearance 

 of a branch of ebony cut transversely! 227. In what woods is the dif- 

 ference between alburnum and perfect more; and in what one is it 

 less marked? 



