112 THE PLANT CELL 



parenchyma zx^Aprosenchyma. Between them no sharp distinction 

 can be made, but the former usually consists of cells which are in- 

 dividually much the same in length, breadth and thickness, and 

 each cell is united to its neighbours by broad flat ends and sides. 



Although in young tissues all the cells are in complete contact 

 at all points of their surfaces, in permanent parenchymatous tissues 

 the common cell-walls of adjoining cells frequently separate from 

 each other at the angles and give rise to intercellular spaces (/, Fig. 

 48), which are generally filled with air. It is important to note, 

 however, that in some cases intercellular spaces arise through the 

 complete dissolution or drying-up of masses of cells in which 

 instances the cavity left is most commonly filled with gums, oils, 

 resins and other excreted products. 



The cells of prosenchymaious tissue are long and pointed at 

 both ends ; moreover, the ends dovetail between each other and 

 fit closely without intercellular spaces. Prosenchymatous and 

 parenchymatous tissues, whose cell-walls are thickened and hard, 

 are distinguished as sclerenchyma. 



Ex. 60. — Take one of the inner fleshy leaves of an onion bulb, and, after 

 making a shallow cut into the surface with a sharp knife, tear or strip off a 

 small portion of the ' skin.' Place it in eosin solution or red ink for a few 

 minutes : then wash it and mount in a. drop of water on a. glass slide. 

 Examine with a microscope, first using a low, and subsequently a higher 

 power. Notice and make drawings of the cells, their cell-walls, stained 

 nuclei, protoplasm, and vacuoles. 



Ex. 51. — Cut very thin slices of a turnip with a sharp razor and examine 

 in a similar manner ; observe the intercellular spaces between the cells. Cut 

 slices of a coloured beet-root : examine without staining, and notice the 

 coloured cell -sap. 



Ex. 62. — Make and examine a section of Elder pith : observe the form and 

 size of the dead cells and also the thickness and markings of the cell-walls. 



Ex. 53. — Make transverse and longitudinal sections of the wood of an 

 ordinary safety match, notice the thickness and markings of the cell-walls. 

 Examine in a similar manner pieces of other common woods. 



Ex. 54. — Cut thin slices of the leaves or any green part of a plant : 

 examine the cells and notice the greenness is not due to coloured cell-sap, 

 but to the existence of numerous small green chloroplasts. 



