56 VEGETABLE HISTOLOGY. 



chlorophyll bodies. In the fresh unstained cell these are green. 

 The chlorophyll granules give the green color to leaves, etc. 



Another difference is the presence of small intercellular 

 spaces between the cells, not found in the onion epidermis or any 

 epidermis in fact. Starch grains also are often present, which 

 assume a deep blue color with iodine, appearing almost black. 

 Under high power the walls that have been stained blue by 

 chlor-zinc-iodine appear finely punctate with nearly colorless 

 dots. These are thin places or pits in the walls. Unlike the 

 epidermal cells of the onion, parenchyma cells are nearly always 

 globular, as may be seen from the cross and longitudinal sec- 

 tions of the Geranium stem (Fig. 35.) 



Parenchyma cells are not always globular and closely packed, 

 but occur at times in modifications, both as to shape as well as 

 arrangement. These modified forms are 



Stellate, or star-shaped cells. 



Folded the cell-walls have internal folds. 



Spongy the cells are very loosely arranged. 



Palisade the cells are elongated and arranged like posts, 

 seen in leaves. 



Pitted the cell-walls marked by thin places of various dimen- 

 sions and shapes. 



Folded cells will be seen later in pine needles, spongy and 

 palisade cells in leaves. For pitted cells, several plants might 

 be chosen, but a convenient one is the plant known as the Sago 

 Palm (Cycas revoluta). 



Examine a cross-section of the petiole unstained in water. 

 Under high power thick-walled rounded parenchyma cells will 

 be found with a number of transparent, rounded areas looking 



Fig. 36. Pitted parenchyma cells. 



like holes in the wall. These are thin portions of the otherwise 

 thickened walls and not holes. On the edges the pits cause a 

 beaded appearance (Fig. 36). Phloroglucin shows that the 

 walls are somewhat lignified, giving a red color. 



Beautiful permanent mounts may be made by staining in 

 aqueous fuchsin solution, passing the section through 70 per 

 cent., 90 per cent, and absolute alcohol, then into eosin oil of 

 cloves for ten or fifteen minutes and finally mounting in balsam. 

 The thin areas of the wall will be stained pink by eosin and the 

 thicker portions red by fuchsin. 



