ROOTS 31 



Make a drawing to illustrate all the points above suggested 

 (1—4). Make a careful study of longitudinal sections through 

 the centers of the tips of very young roots of the hyacinth or 

 the " Chinese sacred lily." ^ Sketch one section. 



Make a study of the roots of any of the common duckweeds, 

 growing in nutrient solution (No. 1, Exp. XV) in a jar of water 

 under a bell glass, and note the curious root pockets, which here 

 take the place of root caps. 



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

 Schenk, Karsten, 1. 



19. structure of the central cylinder of a monocotyledonous root.* * Cut thin 

 cross sections of the adventitious roots of onion or hyacinth near their bases. ^ 

 Examine these in water with a power of two hundred or more diameters. 



Tlie central cylinder or stele shows in the cross section as a nearly circular 

 area containing a few large openings and many smaller ones. The largest open- 

 ings are usually only one or two in number and represent the large vessels 

 cut across. These are tubes with a diameter of yj^ to ^l-g of an inch, with 

 ladder-like markings (seen only in the longitudinal section) on their walls. 

 Radiating away from these are the openings of (in the onion) six other ves- 

 sels of about half the diameter of the central vessels and with similar mark- 

 ings. Just outside of each of the six vessels is an irregular group of much 

 smaller vessels with spiral markings (seen on longitudinal section). The 

 openings of the vessels form on the cross section of the central cylinder an 

 irregular six-rayed star, and the spaces between the rays are mainly filled by 

 sieve tubes or soft bast, separated from the vessels of the wood system by 

 parenchyma cells. The outermost portion of the central cylinder consists of 

 a single layer of cells constituting the pericycle, and this is surrounded by 

 the innermost layer of the primary cortex, the endodermis. 



Reference. Strasburger-Hillhouse, 6. 



20. Structure of the dicotyledonous root ; secondary thickening.' The struc- 

 ture of very young dicotyledonous roots is often similar in most respects 

 to that of the onion root (Sec. 19).* Secondary thickening (Principles, Sec. 80) 



1 Narcissus Tazetta, var. orientalis. 



2 These roots may be obtained from an onion or a hyacinth bulb set in a tum- 

 blerful of water and left in a warm place until the roots are well developed. They 

 may also be taken from hyacinth plants growing in pots, by inverting the latter, 

 removing the contents, an(i replacing the plant when the needed material has been 

 secured from it. 



8 This section may to advantage be deferred until after Sec. 31. 

 * Good materials for study are roots of Ranunculus, bean, or (very young) 

 grapevines. 



