STRUCTURAL VARIATIONS IN HOMOLOGOUS CELLS 



161 



developed. A selection of the results is presented in Table XIV, chosen 

 from a more abundant set of data (47(e)). It will be noted that the 

 angle in the table is called the "standard" angle. This refers to the fact 



TABLE XIV 



The standard angle Q^.^for tracheids of known length 



{the unit of breadth is 1 uni t= 24 fi, 

 and 



for length 1 unit=lA fx) 



selected at random from a much larger body of data. 



a = Annual ring from which tracheid is chosen. 

 b= Length of tracheid. 

 c= Breadth of tracheid. 



d=0i.oo 



e= Average Q. 



that in any tracheid the angle varies along the length of a cell so that the 

 spiral becomes steeper towards the tips. Fortunately the angle Q at any 

 point varies with the breadth b of the cell at that point in such a way 

 that Z>/sin d is roughly constant. It is therefore possible to calculate for 

 any tracheid the value which d would have if the tracheid were of some 

 standard breadth not far removed from the real breadth. The standard 

 II 



