64 



SUGGESTIONS FOR LABORATORY WORK 



(h) a sinp:le superficial layer bearing hairs, the 

 epidermis. 



Make drawings of all the tissues observed. 



Cut sections from older parts of the root, and compare witli 

 those already examined. Kote the formation of cai)tbiu))i 

 in the parenchj-ma internal to the pliloem groups. To the 

 division and growth of these cambium cells is due the 

 secondary thickening of the root. Do the older sections 

 exhibit epidermis? cortex? 



If any of the sections pass through the origin of latai^al i-oots, 

 observe particularly how these originate. Are tliey 

 formed on the surface of the main root, or do they arise 

 from the deeper tissues ? How is their position related 

 to that of the primary xylem groups ? 



Root of Maize. 



In making sections of the root of Maize, the directions already 

 given for the Bean may be foUow^ed, and a comparison 

 instituted betvs'een corresponding sections. Note that 

 there is much less difference between the roots of these 

 plants than between their stems, so far as minute struc- 

 ture is concerned. 



Apex of Root. Cut a longitudinal median section through 

 the apex of a j^oung root. Observe with a high power, 

 and note the root-cap, a rather loose mass of parenchyma 

 covering the tip. Kote the boundary laj-er of cells on 

 each side of the root ; this is the dermatogen, or nascent 

 epidermis. Enclosed by this is a tissue of manj- layers, 

 the nascent cortex, and known as periblem. Within 

 the periblem is the plerome-cylinder, from which the 

 vascular ring of xylem and phloem bundles, observed in 

 previovis sections, is derived. 



Make drawings of the tissues observed. 



Stem of Bean. 



In a cross-section of an internode of the stem make out the 

 following parts, commencing at the centre : 



(a) A central cavity (unless the stem is ver3- j'oung) 



caused by the tearing asunder of the central 

 parenchyma as the outer parts of the stem 

 enlarge. 



(b) The parenchyma of the pith around the cavity. 



(c) The fibro-vascular bundles arranged in a ring 

 outside (b). Study the structure of a bundle, 

 commencing at the narrow end next the centre, 

 and observe in order : 



(1) Comparatively large o])enings with thick 

 walls. These are vessels of different kinds, the 

 larger ones being pitted (as will be seen in a Ion- 



