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Practical Plant Biology. 



whitish cords much tougher than the fundamental tissue. These 

 are the conducting tracts or vascular bundles. It is possible to 

 isolate one of these cords and pull it out of the softer fundamental 



tissue and trace it upwards 

 or downwards in the stem. 

 Microscopic investiga- 

 tion reveals the finer details 

 of structure. Here as in 

 the ends of the branches of 

 the Pine the fundamental 

 tissue is divisible into 

 cortex, medullary rays and 

 pith. The surface of the 

 stem is formed by an epi- 

 dermis, one layer of cells 

 thick. The outer walls of 

 these cells are coated over 

 with thin cuticle, which 

 forms a more or less water- 

 proof and impermeable 

 membrane over the whole 

 stem. The cuticle and the 

 epidermis are perforated 

 here and there with 

 stomata, each guarded by 

 a pair of cells. These 

 guard-cells are the only 

 cells of the epidermis 

 which possess chloroplasts. 

 The other cells of the epi- 

 dermis are colourless. 

 Usually one can see a 

 nucleus and a lining film 

 of cytoplasm in each. 

 Here and there isolated 

 cells of the epidermis grow 

 out at right-angles to the 

 surface as tapering spine- 

 like hairs. Within the epidermis is the cortex. It is formed of 

 thin-walled cylindrical cells, with rounded ends, set parallel to the 

 axis of the stem. These cells contain the usual cytoplasmic lining 

 in which are embedded a nucleus and many chloroplasts. A large 

 vacuole occupies the middle of the cell. Between these cells are 



FIG. 73. Ranunculus bulbosus. 

 Sowerby.) 



(After 



