S'2 STRUCTUKK AND PHYSIOLOGY OF SEED PLANTS 



soon occurs in the roots of dicotyledonous trees and shrubs, and the structure 

 of such roots considerably resembles that of the stem, except that pith is 

 frequently lacking. 



With the lens examine cross sections of large roots of any hardwood tree. 

 Note the annual rings of wood and their porosity, due to the presence of 

 many and large vessels. The cortical part sometimes (as in sassafras) forms 

 a thick bark. 



With the microscope examine thin cross sections, stained with phloro- 

 glucin (Sec. 12, D), of the tap root of a seedling hardwood tree not more 

 than a year old.i Use first l.p., then m.p. Note the division of the root 

 into a cortical region or bark, wood, and (sometimes) pith. Note the relatively 

 small amount of wood in the younger portions of the root, increasing in the 

 older parts. Make drawings to illustrate this point. Make a drawing of a 

 (luarter or less of one of the older sections, showing the distribution of mate- 

 rial from center to exterior. In your drawing color the lignified hard-bast 

 fibers of the bark (Sec. 29, C) and the wood fibers, to distinguish them from the 

 non-fibrous parenchyma which makes up much of the bulk of the young root. 



If the material was collected in the autumn or winter, test a section with 

 iodine solution for starch, and if any is found describe its distribution. 



References. Strasburger-Hillhouse, 6 ; Strasburger, Noll, Schenck, 

 Karsten, 1 ; Tschirch, 83. 



21. Examination of a fleshy root. Cut a parsnip across below 

 the middle, and stand the cut end of the upper part in eosin solu- 

 tion (Sec. 169) for twenty-four hours. 



A. Examine by slicing off successive portions from the upper 

 end. Sketch some of the sections thus made. Cut one pars- 

 nip lengthwise and sketch the section obtained. In what 

 portion of the root did the colored liquid rise most readily ? 

 The ring of red marks the exterior of the central cylinder 

 in contact with the cortical portion. To which does the 

 main bulk of the parsnip belong ? 



B. Cut thin transverse sections from an eosin-stained parsnip 

 and notice how the medullary rays run out into the cortical 

 portion, and in those sections that show it find out where 

 the secondary roots arise. 



1 These may be pl:iiite(i lor the purpose, but usually it is easy to find plenty of 

 young seedling cherries, birches, elms, ashes, maples, etc. 



