MARKINGS OF THE WALLS OF CELLS. 



37 



distribution of the secondary deposit. They are portions of the 

 walls which are either thinner or thicker than the rest. These 

 markings display the greatest variety of forms, many of them of 

 surpassing elegance. The principal kinds occur with perfect uni-j 

 formity in each species or family, and in definite parts of the plant ; / 

 so that, in a multitude of cases, the sort of plant may be as certainly I 

 identified by the minute sculpture of its cells alone, as by more con-' 

 spicuous external characters. They are preserved even when the 

 tissue is fossilized, and the 

 external form, with every 

 outward appearance of or- 

 ganization, is obliterated. 

 Through thin slices and 

 other contrivances, the hid- 

 den structure is revealed 

 under the microscope, and 

 thus the true nature of the 

 earth's earliest vegetation 

 may be often satisfactorily made out. 

 In this way, and by taking advantage of 

 the fact, that the secondary deposits in 

 the cells contain a good deal of mineral 

 matter, which is left behind in the ashes. 

 Professor Bailey was able first to dis- 

 cover vegetable structure in anthracite 

 coal.* The simplest and commonest 

 markings are those which appear as 

 pores or holes, but are really 



45. Dots or Pits, such as those on the 

 cells of the pith of Elder (Fig. 38), and 



* See Silliman's American Journal of Science and Arts, New Series, Vol. I. 



FIG. 31. Magnified cross-section of a small portion of heart-wood of the Plane-tree or 

 Buttonwood (Platanns occidentalis). 32. A corresponding longitudinal section, parallel with 

 the circumference, a, The dotted woody tissue ; the lower ends of the two cells to which the 

 letters are appended are divided lengthwise, so as to show the irregularly thiclrened calibre ; 

 the others are mostly entire, showing the dots : in the cross-section the secondary deposit is 

 seen to form indistinct layers, and some of the dots to form canals of lateral communication, 

 6, Dotted ducts : the middle one in the longitudinal section is obliciuely jointed, c, Medullary 

 ray. 



JIG. S3. Portion of four cells of the woody tissue, with both transverse and longitudinal 

 section, highly magnified, showing the canals or deep pits in the thickened walls, and their 

 apposition in adjoining cells : on the cross-section the layers of deposit are more plainly visible. 



4 



