229 



All the elements of the wood, includin.u' even the wood fibres, have 

 their Inmina tilled witli a l)rown to black solid coloring matter. The walls 

 of the elements are not impregnated with the color, and consequently 

 stand out distinctly, so that their peculiarities are easily observed. 



The chief peculiarity of Leopard-wood is the presence of sclerenchym- 

 atous tyloses. Thyloses or tyloses, as tliey are more commonly called, 

 are ingrowths of parenchymatous cells into the cavity of the tracheae. 

 When a trachea is adjoined by parenchyma, the parenchyma retains its 

 protoplasm after the trachea becomes empty; as the parenchyma exerts 

 pressure on the non-resistent walls of the trachea, the parenchyma pushes 

 into the cavity of the trachea through a pit or weak spot, forming a short 



Leopard-wood. Trans. Sect. ( x 80 ) 



tube. The tube may be the only one at that part of the trachea, or there 

 may be so many that there is a series of tubes lining the entire cavity. 

 These ingrowths may make no fiirther progress, but the more common 

 method of development is tlie formation of a wall at the junction of the 

 tracheal wall, cutting off the ingrowths. These ingrowths may then 

 carry on cell division, forming a mass of parenchyma filling the lumen of 

 the trachea. Tyloses form in many Dicotyledons as a regular phenom- 



