LABORATORY STUDIES 63 



small diameter. Further down, part of these strands will be 

 found to consist of tracheary tissue. 



(6) Study a vascular bundle of the radial type, by making 

 cross-sections of the larger roots of corn, iris, hyacinth, or of 

 the main roots of seedlings of bean, pea, sunflower, etc. Note 

 the number of xylem plates, location and extent of phloem, the 

 endodermis, pericycle, etc. 



(c) Make longitudinal sections of the same kinds of roots, 

 and identify the tissues shown in cross-section. 



(d) Using a bean seedling, in which lateral rootlets have 

 begun to show, make numerous cross-sections, so as to find such 

 rootlets in various stages of development, and study their or- 

 igin and mode of emergence. 



(e) The concentric type of bundle may be studied best in 

 cross-sections of the rhizomes of the brake (Pteridium aqui- 

 linum). Make a longitudinal section also, so as to identify the 

 tissues present. 



(/) Vascular bundles that may perhaps be assigned to the 

 concentric type may be studied in cross and longitudinal 

 sections of the stems of Selaginella and Lycopodium. 



(g) Make cross and longitudinal sections of the stem of 

 Indian corn, sugar cane, Smilax herbacea, or other mono- 

 cotyledons, for vascular bundles of the closed collateral type. 

 Note their distribution in the stem. 



(h) Open collateral bundles may be studied to advantage in 

 the younger internodes of clover and alfalfa, or the upper ones 

 of sunflower. Note the arrangement of the various xylem 

 elements. Note how the bundles are distributed in the stem. 



(i) Study the lower internodes of the same plants, for secon- 

 dary thickening. Note the differences between the secondary 

 xylem and that formed in -the bundle before the secondary 

 thickening had begun. Note the secondary vascular bundles, 

 interfascicular cambium, etc. 



(/) Make and study a cross-section of a two-year-old twig of 

 basswood, elm, or other tree. Note the growth rings, and in 

 cross and longitudinal sections determine their structure. 

 Study the primary and secondary medullary rays. 



(k) For bicollateral vascular bundles, the best objects are 

 the stems of Cucurbitaceae, e.g. squash, cucumber, etc., 

 although they are found also in the Solanaceae, e.g. younger 

 parts of the stems of petunia, potato, etc. 



