FORMS OF CELLS. 
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convenience of study, as follows: (1) parenchyma cells, 
(2) mechanical cells, (3) conducting cells and (4) pro- 
tection cells. 
I. PARENCHYMA. 
Under the head of parenchyma are included those 
cells which are nearly isodiametric and thin-walled, 
the walls consisting of cellulose lamellae. They may 
contain both organized and unorganized cell-con- 
tents. According to the function and nature of con- 
tents, three kinds of parenchyma cells are recognized: 
(a) CMorophyl-parenchyma or assimilation parenchyma, 
which is rich in cliloroplastids and occurs in leaves 
and all green parts of the plant. ( b ) Reserve paren- 
chyma occurs in seeds, roots, rhizomes, etc., and contains 
starch, aleurone grains, fixed oils and other reserve 
materials. The parenchyma in stems and leaves of 
various of the orchids, as well as that of plants of arid 
regions, which store water, may be included in this 
group, (c) Conducting parenchyma assists in the trans- 
ferral of food from one part of the plant to another. 
Besides these forms of parenchyma there are some 
special kinds which may be mentioned, as the some- 
what branching cells in leaves, and in the stems of 
various marsh plants, as in species of Juncus and 
Pontederia. In calamus, large intercellular spaces are 
formed, and these may be mistaken for the cells them- 
selves. 
II. MECHANICAL CELLS. 
Mechanical cells include all those cells which serve 
to keep the various parts of the plant in their proper 
positions one with reference to the other, and which 
enable it to withstand undue strain and pressure. 
There are two principal forms of mechanical cells, 
namely, collenchymatous and sclerenchymatous. 
