144 ANATOMY OF STEM, ROOT AND LEAF 



include the root-hairs : mount it in water and examine first with a low and 

 then with a high power. 



Ex. 70. — Cut transverse sections of a young root of a bean or pea through 

 the region bearing root-hairs, and place them for twenty minutes in ' Eau 

 de Javelle ' (Ex. 75) : wash them and mount in glycerine. 



Examine with a low power ; observe and sketch the piliferous layer bear- 

 ing root-hairs, the parenchymatous cortex and the central vascular cylinder. 



Examine with a high power and make drawings of the wood and bast 

 strands, pericycle and endodermis. 



Ex. 71. — Cut transverse sections of the older parts of the root of a pea or 

 bean, near where the lateral roots are just beginning to appear. Clear with 

 'Eau de Javelle' and mount in glycerine. Make a sketch of a section 

 which shows the lateral roots boring their way through the cortex. 



THE aREBN FOLIAGE-LEAF. 



The leaves are built up of the same tissues as the stems and 

 roots, namely, of epidermis, vascular bundles, and ground-tissue, 

 but the arrangement and constitution of these tissues are different. 

 The vascular bundles coming from the stem run into the leaf 

 and in dicotyledons branch repeatedly in one plane to form a fine 

 net-work of strands, which conducts sap to and from all parts of 

 the leaf and at the same time acts as a firm framework for 

 the support of the soft ground-tissue. In monocotyledons the 

 main branches of the bundles which enter a leaf generally take 

 a parallel course and are connected by smaller oblique strands. 



The bundles of the leaves are always closed, there being no 

 need for an active cambium in parts of the plant which are of 

 such limited growth. 



As the bundles curve out of the stem into the leaf without 

 twisting, the wood comes to lie nearest the upper surface of the 

 leaf, and the bast nearest the lower surface. 



With the exception of the absence of cambium the larger 

 vascular bundles of the leaf resemble those of the stem. The 

 wood of the finer strands, however, consists of spirally thickened 

 elements only, and the extreme tips of the bundles which in 



