6 TIMBER AND TIMBER TREES. [CHAP. 
and when so used in decks, flooring, &c., rendering it 
dangerous to walk upon. 
In the transverse section of a tree will be found a 
number of lines radiating from the centre and pre- 
senting a star-like appearance. These are the medullary 
rays of the botanists, but are best known to carpenters 
as the silver grain, or felt (2, Fig. 3). This peculiarity of 
appearance is due to thin plates of compressed cellular 
tissues, which usually run continuously from the pith to 
the bark. Although, as a general rule, this is the case, 
yet in some 
species a se- 
condary series 
is found, over- 
lapping or 
scarfing by, 
but very sel- 
dom touch- 
ing, the pri- 
mary rays (4, 
Fig. 3). If, 
therefore, 
we carefully 
FIG. 3. examine the 
smooth — sur- 
face of a transverse section of the stems of most trees, 
we can generally trace these thin plates or rays. They 
can be seen to great advantage in the Beech, and, more 
or less, in all the varieties of Oak ; but they are far less 
distinct in the Lime, Yew, and Chestnut, and in the 
Firs and Pines they cannot be traced, although botanists 
believe them to be present. 
Before converting or employing most kinds of woods, 
particularly in dealing with unseasoned timber, it will be 
