10 THE ANATOMY OF WOODY PLANTS 



structure may be more easily discerned . External is the single layer 

 of the epidermis, made up of cells with thick, heavily pitted walls. 

 With the greater magnification employed, the cellular organization 

 becomes very obvious. Underneath the epidermal layer is situated 

 the fundamental system, in turn clearly outlined against the 

 fibrovascular tissues by a striking boundary composed of a single 

 series of cells with dark tanniniferous contents. This is the most 

 internal layer of the fundamental system and is known either as 

 the endodermis or as the phloeoterma (the latter term in its ety- 

 mology indicating the inner layer of the cortex or fundamental 

 tissue). The fundamental tissues are characterized locally by 



FIG. 7. A portion of a transverse section of the rootstock of Pteris aquilina 

 more highly magnified, showing the three tissue systems. 



certain bands of dark-brown skeletal tissue, which are very char- 

 acteristic of the lower vascular plants and subserve to a large extent 

 the mechanical function which in the higher plants is attended to 

 by the fibrovascular system. Those regions of the fundamental 

 system which are not mechanical in their nature take over the 

 function of storage and are crowded with granules of starch forming 

 a cordon around the periphery of the cells. Centrally the elements 

 of storage show the presence of a dark-brown substance in the 

 region of the vacuole. This is tannin-like in its nature and is 

 commonly present in the fundamental system of ferns. The 

 fibrovascular structures stand out sharply from the rest of the 

 tissues and are obviously much more complicated in their organiza- 

 tion than are those previously considered. The fibrovascular aggre- 

 gations of cells are of the greatest anatomical importance, both 

 because their very complexity of structure supplies many valuable 



