CHAPTER X 

 THE FUNDAMENTAL TISSUES 



It has been indicated above that the epidermal tissues constitut- 

 ing the external boundary of the plant toward the outer medium 

 have relatively slight value from the standpoint of evolutionary 

 anatomy. The same statement may be made (with less emphasis) 

 concerning the category of cellular organization, known as the 

 fundamental tissues. This group is on the whole much more 

 extensively developed and more clearly defined in the lower forms 

 of vascular plants than in the case of those higher in the scale. 

 The more massive presence and the more distinct individualization 

 in the fernlike representatives of vascular plants naturally carry 

 with them a higher degree of histological differentiation. The 

 fundamental system is definitely bounded internally by the endo- 

 dermis (phloeoterma of Strasburger) in most of the lower groups of 

 plants, while in more advanced vegetable organisms the limits be- 

 tween the fundamental and fibrovascular systems are often obscurely 

 indicated except in that most conservative of all organs, the root. 

 Externally the limits of the fundamental system are usually clear 

 unless the multiplication of the epidermal layer conceals the situa- 

 tion. Occasionally in roots the fundamental system is sharply 

 marked off toward the epidermal system by the presence of a well- 

 developed limiting layer, the exodermis, which externally is the 

 counterpart of the endodermis, indicating the internal confines of 

 the cortex. 



The accompanying figure (Fig. 96) of the subterranean stem 

 of the bracken fern will illustrate both the definite limits and the 

 considerable degree of specialization and consequent physiological 

 importance of the fundamental tissues. It is clear that within the 

 epidermis and external to the fibrovascular bundles there is present 

 a large amount of cellular substance. This is distinctly differ- 

 entiated into two categories namely, sclerotic or supporting 

 tissues and storage parenchyma. The former is present in two 



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