3IO A TEXT-BOOK OF BOTANY. 



commonly referred to as the cortex, and is either homogeneous 

 or divided into two zones, the outer or peripheral being composed 

 of thick-walled cells which naturally belong to the hypodermis 

 and an inner or internal strata made up of thin-walled cells. The 

 cells of the cortical parenchyma may contain starch, calcium 

 oxalate, calcium carbonate, and there may be associated with them 



Fig. 170. Cross-section of the primary root of a germinating plant of Phaseolus 

 muUiflorus, showing development of secondary structures: p, group of primary vessels; 

 g, larger tracheae of secondary development formed between the four primary strands of 

 xylem; b, the four groups of phloem alternating with the four initial groups of xylem and 

 beneath which secondary tracheas are forming (g') ; pc, pericambium (pericycle), a layer of 

 cells beneath the endodermis (s). A few layers of cortical parenchyma are shown outside 

 of the endodermis. In the middle is a well-developed pith (M) which sometimes is developed 

 in roots. — After Sachs. 



secretory cells or receptacles. Immediately beneath the innermost 

 layer of cortical parenchyma is a distinct layer of cells usually 

 considered part of the cortex and knowm as the endodermis. It 

 consists always of a single layer of cells, without any intercellular 

 spaces, and the radial walls show in transverse section Casparyan 

 spots,^ depending upon a local folding of the cell-wall, which is 

 here suberized. In the course of time the cell-walls of the en- 

 ^ " Physiologische Pflanzenanatomie," by Dr. G. Haberlandt, p. 245. 



