46 GROUPS OF TISSUES, OR TISSUE SYSTEMS 



(Equisetum). This is a difficult section to make, but if suc- 

 cessful the growing point, with its single apical cell, can be 

 studied. Sometimes this can be seen better by making 

 successive, very thin cross-sections at the tip of a fern root. 

 In this case, the apical cell will be seen in transverse view. 



((/) IVIake a longitudinal median section through the growing 

 points of a stem and a root of a Flowering Plant. (Stained 

 microtome sections are preferable to hand sections since they 

 are thinner and more likely to show the desired features.) 

 Note that all of the tissue near the tip is meristem. Observe 

 the three regions, dermatogen (epidermis), periblem and 

 plerome. Trace them to their origin. On the root section, 

 note also the root cap and its origin. 



61. The tissues produced from the primary meristem 

 in the manner described above have definite functions 

 to perform, and occupy definite positions in the plant 

 body. The outer layer or epidermis is set off as a boun- 

 dary tissue; other cells are developed into the skeletal or 

 supporting tissues, still others are for transportation of 

 water and food, while the remainder of the cells are at 

 first not so clearly differentiated for special functions. 

 This less differentiated group of tissues may eventually 

 fulfill various functions depending upon the part of the 

 plant they occupy, the nature of the plant, etc. Thus 

 they may be food making, as in leaves; for storage pur- 

 poses, as in tubers, many roots, some pith, etc. ; protective, 

 as in the shell of nuts where the tissue is changed to 

 sclerenchyma. 



62. According to the kinds of tissues and functions, 

 it is customary to differentiate several so-called ''tissue 

 systems.'' These may be defined as aggregations of 

 elementary tissues, forming definite portions of the plant 

 and with a definite function. It is at once evident 

 that tissue systems cannot be distinguished where tissues 

 are not yet differentiated. In fact, we usually speak of 

 them only in connection with the higher plants. 



