I 10 



ANATOMY OF THE GYMNOSPERMS 



tr. 



-tr.w. 



.fr.w. 



genus, in which they form a specific character of definite value, 

 and it is therefore of importance that they should be described 

 somewhat in detail. 



In a transverse section (plate 18) the idioblasts, recognizable 

 by their conspicuous crystals, may be seen scattered through 

 the entire section without special reference to either the spring 

 or the summer wood. Under a high degree of amplification it 

 will be seen that they are often single, but quite frequently they 



are grouped in radial series 

 of two or three, in which case 

 one is generally much larger 

 than the others (fig. 34, a}. 

 The form is narrowed tangen- 

 tially and extended radially so 

 as to be approximately lenticu- 

 lar, and the cavity is usually 

 pretty well filled with a com- 

 pound crystalline mass. The 

 idioblast is situated in the 

 line of one of the radial rows 

 of tracheids, the continuity of 

 FIG. 34. GINGKO B i LOB A. , trans- which it interrupts. It is usu- 



verse section showing the occurrence a |Jy mucn larger than the ill- 

 and form of a crystallogenous idio- . . . , , 



blast;*, tangential section of the same, dividual wood tracheid, from 



tr., tracheids; tr.-u>., tracheid walls; i., which it also differs ill the char- 



idioblast; /,., idioblast wall; cr., acter o f the cell wall, which is 

 crystals. X 233 



very thin and not infrequently 



shows a want of continuity suggestive of obliteration in the course 

 of development. In a radial section the idioblasts are usually of 

 an isodiametric form, more rarely elongated longitudinally, and 

 the compound crystalline mass somewhat more than half fills the 

 cavity. In this section the walls are seen much better than in 

 any other, and the relations of the idioblasts to one another are 

 well exhibited. In a tangential section (fig. 34, b) the wall is also 

 well displayed. The individual idioblasts are lenticular in form 

 and the crystalline mass completely fills the cavity transversely, 



