6G 



SUUilESTlONS FOR LABOliATOliY WollK. 



nearest the centre of the bundle spiral, the other 



annuUir. 

 (2) Around and between the two large vessels, thirk- 



walled tissue consisting of tracheids. 

 (;i) Below the jjitted vessels and around the smaller 



vessels, thin-walled parenchyma. These three 



elements make up t lie xylem portion of the bundle. 

 (4) On the opposite side of the space separating the 



pitted vessels, a mass of soft bast (the phloem 



portion of the bundle). 

 (.")) Surrounding all the above elements, a thick sheath 



of sclerenchyma. 



Make a draiving of the bundle. 



In longitudinal sections, make out all the above tissues, and 

 draw them. 



In longitudinal sections of the stems of both Bean and Maize, 

 cut so as to pass through a node or insertion of a leaf, 

 endeavour to trace the course of the vascular bundles^ 

 and to make out the relation of the bundles of the stem 

 to those of the leaf. 



Leaf of Bean. ' 



A bit of leaf may be held in a slit in a piece of elder-pith, and 

 thin sections made at right angles to the surface. Some 

 of the sections may be immersed in alcohol for a time to 

 drive out air, bitt as this process also dissolves the 

 chlorophj'll, other sections should be examined as cut. 

 The}' maj' be mounted in water or dilute glycerine. 



Note ill order : 



(a) Tlie transparent upper layer, the epidermis the 



outer limit of which is the cuticle. 



(b) Below this, rather long chlorophj-ll-bearing cells 



standing on end, the palisade tissue. 



(c) Still lower, some irregular layers of chloroph^'ll- 



bearing cells, with intercellular spaces, the 

 spongy parenchyma. 



(d) Thetransparent lower layer, the epidermis. 



(e) Possibly sections of veins. In these try to make 



out the elements of fibro-vascular bundles. 



(f ) Note the forms of hairs if any appear. 



Make drawings of the sections. 



Tear off with forceps a strip of epidermis, and mount as before. 



Note the absence of chlorophyll, and the very irregular outline 

 of the cells. Find also examples of stomata, more espe- 

 cially in the lower epidermal layer. Observe if possible 

 the guard-cells, and find out in what particular, if any, 

 they differ from the other epidermal cells. 



