PLANT TISSUES 117 
more or less isodiametric to irregular and elongated forms. The 
cells always contain chloroplasts or plastids, in whose pores may 
be found some other coloring substance. Good examples of 
assimilation tissue are seen in the green column-shaped cells 
below the upper epidermis of foliage leaves which, because of 
their shape, are termed “‘falisade parenchyma cells’ and in the 
green rounded to irregular-shaped cells beneath the palisade 
parenchyma of foliage leaves which, because they are more 
loosely arranged around air-spaces, ¢ 
are termed “‘spongy parenchyma cells.” “\~—— 
(See Fig. 166.) 
ConpucTING PARENCHYMA.— 
This type of parenchyma functions 
in the rapid translocation of food 
materials to distant regions in the 
plant. It includes the wooed paren- 
chyma cells of the xylem which convey 
a portion of the crude sap (water 
with mineral salts in solution) and 
the phloem parenchyma (soft bast) 
which transports the elaborated sap 
: : Fic. 58.—Transverse section of 
(carbohydrate and proteid material part of leaf-stalk of a begonia. 
in solution). Conducting paren- ¢, Epidermis; c, cuticle; B, collen- 
iia ‘differ fram those of chyma, with walls thickened at 
chyma ce. the angles, v;_ chl, chloroplasts. 
ordinary parenchyma in being (¢4),¢ after Vines.) 
usually more elongated and in con- 
ducting soluble food materials with greater celerity. 
RESERVE PARENCHYMA.—This resembles ordinary paren- 
chyma in many particulars of structure but differs from it mainly 
by its cells being filled with starch, protein crystals, or oil 
globules. It is usually found in seeds, fleshy roots, or under- 
ground stems such as tubers, corms, and bulbs. 
CoLLENCHYMA.—This form of tissue is characterized by its 
cells being prismatic, more elongated than ordinary parenchyma, 
with soft, plastic walls of cellulose thickened in areas, usually 
in their angles, but sometimes on the tangential walls or on 
the sides abutting air-spaces, with a colloidal substance. The 
thickened areas are in the form of longitudinal strips. The 
