FORMS OF THE DISK 85 



the circle to which it is adnate. The simplest manifestation of the disk 

 is that of a mere swelling or ring (Fig. 253) at the summit of the torus; 

 its greatest that in which it becomes an elongated cup or tube. Either 

 form may be entire or more or less divided, from that with a mere sinu- 

 ately lobed margin (Fig. 263) through the toothed and lobed (Fig. 265) 

 to that consisting of entirely separate divisions (Fig. 264). It may be 

 regular, as in the above illustrations, or very irregular (Fig. 261), and 

 cohesion may exist between some of its divisions while the others are 

 distinct (Fig. 262). The lower portion may be adherent while the 

 upper, lobed or entire, is free (Fig. 266). It may be itself appendaged, 

 and it may or may not be glandular in nature. Finally, we note that 

 the disk may be double, its two circles occupying diiferent internodes 

 of the torus. The texture of the disk is commonly thicker than that 

 of the other parts, but it may be laminar. It is, therefore, sometimes 

 easy to mistake a disk for a corolla, aborted stamen-circle, or crown. 

 In all its peculiarities above described, and in the number, size, and form 

 of its divisions and appendages, the disk is characteristic and of the 

 greatest value in classification, either generic, as in the Gesneriaceae, or 

 specific, as in Eschscholtzia. 



