PRACTICAL WORK 3OI 



scope. Note especially the region of short (young) root hairs, 

 each of which arises from a surface cell. Note also the region 

 of primary meristem covered by the root cap, the bare elongating 

 region and the vascular cylinder seen through the semi-transparent 

 cortex. 



(3) Examine the fresh taproot, 2 or 3 inches long, of a 

 Bean seedling. Observe the root cap covering the growing 

 point and the four or more longitudinal rows of lateral roots. 

 Cut the root longitudinally through the centre in the region of 

 origin of the branch roots, and make out with a lens that these 

 arise from the surface of the central cylinder. 



In the older part of the root the cortex can generally be separ- 

 ated from the cylinder by twisting the root so as to break the 

 cortex and then pulling it off. 



(4) Make a low power diagram of a transverse section of a 

 buttercup root taken through the root hair region, and showing 

 piliferous layer, cortex and cylinder, and in the cylinder the cross- 

 shaped xylem with four arms, the ends of which are formed by 

 the narrow tracheids of the protoxylem. Between the arms of 

 the xylem are the four strands of phloem. Put in the boundaries 

 of the tissue regions, but not individual cells. 



With the high power examine the different tissues in detail, 

 and draw a portion of the cylinder, including a segment of endo- 

 dertnis and pericycle, protoxylem, large vessels of the metaxylem (in 

 the centre these still have thin walls cytoplasm and nucleus 

 can sometimes be seen in them), also sieve tubes and companion 

 cells of the phloem, and conjunctive tissue. Starch grains can 

 be seen in the cortex. 



(5) Examine the cross-section of a young Bean root, noting 

 that the outline of the cylinder is not so easy to define as in the 

 Buttercup, the endodermis being less sharply distinguished from 

 neighbouring cells, but on careful examination with the high 

 power the cutin strips of the radial walls can be made out. 

 The xylem strands are not joined in the centre, which is occupied 

 by pith . The thicker walled cells forming the bulk of the phloem 

 are fibres : a few sieve tubes can be seen outside these. In 

 older sections cambium (formed early here) and secondary tissues 

 can be made out. 



(6) Examine longitudinal sections through the centre of the 

 tips of Maize and Bean roots. Note in each root cap, primary 

 meristem, and the growth in size and elongation of the cells as the 

 apex is left. In the Maize especially note the great increase 

 in width of the rows of cells which will form the large vessels, 

 and the stages of development of these. 



