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. 
(d) Make 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. 
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