THE LEA VES. 



(.i, fig. 158). In transverse section the vascular bundles 

 are variously placed, being irregularh' scattered, or (lis[)Osed 

 in one or several groups. 'I'hc single group is most common, 

 with the paired bundles jilaced so as to form a crescent, or 

 even a complete ring, which is tlatteued al)0\'e or triangular. 

 The largest pair is generally median and dorsal (fig. 15S), 

 with smaller ones right and left. 



165. (b) The blade. — In broad leaves, the epidermis of 

 the blade is made up of tabular cells, often with wavy lateral 

 walls (fig. 159). In narrow leaves the epidermal cells are 



Fig. 150.— Surface \ic\v of epidermi.s from under side of leaf of bracken fern [Ptcris), 

 sfiowint: \\a\ V cells, except o\er \eins, r'. where t]ie\- are elongated, st, stomata. 

 Tlie dof in each cell represents the nucleus. Highly magnified.— After Sedg^vick and 

 Wilson. 



longer than wide (fig. 160). Over the veins the cells are 

 elongated parallel with the ^-ein. The epidermal cells are 

 generally lYee t'rom chloroplasts. The epidermis usuall\' 

 consists of one laver, but in some jilants becomes several- 

 lavered, either to serve as additional protection against eva- 

 poration or for use as a water-storing tissue. (^See ^ 44i- ) 



