SEOT. I 



MORPHOLOGY 



147 



thickened lateral walls. While the tracheal tissues are engaged in providing for 

 the conduction of water, the duty of conducting and storing the products of 

 assimilation, in particular the carbohydrates, is performed by the parenchymatous 

 tissues of the wood. Both forms of tissue, however, aid in maintaining the 

 rigidity of the plant body, and, in their most extreme development, furnish such 

 elements as the fibre tracheides on the one hand, and on the other the empty wood 

 fibres, which are only capable of performing mechanical functions. 



A, Elemi'iits of the tracheal tissue of the wood ; cliagrammatie. B, Elements of the 

 parenchymatous tissue of the wood ; diagrammatic. For description see text. 



The wood of Dicotyledons is made up of the elements of these two classes of 

 tissue, the tracheal and the parenchymatous, but all the different elements are not 

 necessarily represented in any one kind of wood. 



Drimys, a genus belonging to the Maguoliaceae and two genera of the related 

 order Trochodendraceae, are the only Dicotyledons the wood of which is formed of 

 tracheides only. These Dicotyledons closely resemble the Conifers in structure. 

 In numerous Leguminosae, Willows, Poplars, and species of Ficios, on the other 

 hand, the tracheal tissues are only represented by vessels, which perform the task 

 of water conduction. In the wood strands of these plants there are also present 

 wood parenchyma and a large proportion of wood fibres. The vessels in climbing 

 plants (lianes) are especially wide. 



