152 GENERAL STRUCTURE OF ROOT AND STEM 



elements causing roii^-hiiess may require mieros('()])ical examination 

 for their demonstration, while others are otherwise manifest. 



Ridges and Furrows. — Care must be taken to distinguish between 

 ridging and furrowing of different kinds. One kind is caused by a 

 longitudinal wrinkling in drying, as in young Calisoya (Fig. 425). 

 Another is owing to transverse (as in old Calisaya) or longitudinal (in 

 the same) fissuring (Fig. 427). Another is caused by the elevation of 

 corky ridges, or rows of corky warts, which may or may not become 

 confluent in variable degree (as in Succiruhra, Fig. 426). Fissures may 

 characteristically open in the crest of a ridge or in the otherwise un- 

 changed siu-face. 



Color-markings. — Most color-variegations are due to lichens or 

 other parasites, and those due to lenticels are also very common. A 

 single color or shade of color of the inner surface is rarely characteristic, 

 as it changes very greatly with age in keeping; but a carefully arranged 

 series of them may be made diagnostic in many cases. 



The Inner Surface. — The important characteristics of the inner 

 surface depend upon the projecting bast-bundles caused by contracting 

 medullary rays. Very rarely, indeed, is the surface so free from these 

 inequalities that it can be properly described as smooth. The slightest 

 manifestation of the bundles gives the Striate condition. The striae 

 must be examined as to length, straightness, direction as contrasted 

 with the axis of the bark, apparent interconnection at the end, width, 

 elevation, and sharpness, with the complementary characters of the 

 intervening furrows or pits. Some barks show a tendency to separate 

 into laminae which run obliquely out upon the inner face, appearing 

 there as partially separated tongue-shaped splinters. 



No attempt has ever yet been made to classify the markings of the 

 inner surfaces of dried barks, and to provide a terminology for them. 

 In the absence of this important treatment, it is difficult to teach the 

 details of the subject, except by the use of the actual objects. 



