MORPHOLOGY 



129 



in Maples to some extent superfluous, and it is therefore sparingly developed. In 

 addition to wood fibres the Maple chiefly develops vessels, while the formation of 

 traeheids is restricted to the late wood. The mechanical elements of the wood of 

 the Ivy (Hedera Helix) and Grape-Vine (Vitis vinifera) axe septate wood fibres. In 

 Oaks, Beeches, and in the Sosiflorae wood fibres are absent, and the necessary rigidity 

 is provided for by fibre traeheids. The wood of the Lime (Figs. 145-148) is composed 

 of vessels (Fig. 146, to), traeheids (t), wood parenchyma (p), and wood fibres (I). 



i\ tLt 



Fig. 142. — Tangential section of the late 

 "wood of a Pine, t, Bordered pit ; hn, 

 tracheidal medullary ray cells; sm, 

 medullary ray cells containing starch ; 

 et, pit bordered only on one side ; i, 

 intercellular space in the medullary 

 ray. (x 240.) 



Pig. 143.— Elements of the 

 wood ; diagrammatic, 

 text.) 



tracheal tissue of the 

 (For description, see 



The vessels and traeheids form radial rows, alternating with rows of wood fibres. 

 In the early wood wide pitted vessels are produced, the formation of which after- 

 wards ceases, and in the late wood only traeheids are formed (Fig. 146, t). The 

 annual rings are thus sharply defined (Fig. 146, t). The new vessels of the succeeding 

 spring join the traeheids of the previous year, and in this way a sufficient connection 

 for the water transport is obtained. All transitional forms between vessels and 

 traeheids are to be found in the wood of the Lime. Besides bordered pits, tertiary 

 spiral thickenings are also developed in the trachea] elements. The wood fibres 

 (Figs. 146, 147, 148, I) are relatively thin-walled, with wide cavities and narrow 

 elongated pits, and contain air. The wood parenchyma (Figs. 146, 148, p) forms 

 interrupted tangential bands. 



K 



