32 THE TISSUES OF PLANTS 
the pith cells of one or two year old twigs of apple. These are 
also somewhat thick-walled. 
41. Sclerenchyma is the name given to a tissue con- 
sisting of more or less rounded or polyhedral, usually 
not much elongated, thick-walled cells whose function is 
to give support or protection to other tissues. These 
cells originate from meristem by the thickening and 
lignification of the walls, passing through an intermediate 
parenchymatous stage. During the process numerous 
spots on the walls remain thin so that 
eventually they show as canals from the 
original outer wall. These canals or pits 
Fic. 11.—Sclerenchyma correspond in adjacent cells. Upon 
(hickory put). reaching their final development the cell 
contents die. Sclerenchyma cells are often called stone 
cells. They are found in seed coats, nut shells, bark, 
etc., where protection or support is required. 
42. Of a much different type from the foregoing are 
those tissues consisting of elongated cells with more or 
less thickened walls whose function is the mechanical 
strengthening and support of the plant body. To per- 
mit bending while at the same time retain- 
ing their supporting function they are more ° 
or less elastic, a characteristic less marked 
in the short-celled sclerenchyma whose func- 
tion is protection or only local support. .. is ain 
We can distinguish two types of these sup- chyma, 
porting or mechanical tissues, collenchyma and fibrous 
tissue. 
43. Collenchyma. Directly beneath the epidermis of 
many plants are found smaller or larger strands of elon- 
gated cells whose longitudinal cell walls are thickened at 
the angles where three or more cells come in contact. 
— ie gid 
