2696 Journal of Applied Microscopy 



3. Under low power draw part of a section showing the epidermis with epi- 

 dermal hairs, the layer of colenchyma immediately below this, the parenchyma 

 with resin passages, the vascular bundles with cambium layer, the medullary 

 rays, and the central pith. 



4. Under high power draw a single vascular bundle, selecting one of the 

 narrow, oval type. Represent in order the external bundle of sclerenchyma, the 

 phloem, the cambium, and the xylem usually in a double layer. 



5. Notice the mechanical principles involved in the structure of the stem 

 and the vascular bundle. Compare with a T railroad rail. 



(b) Pntnpkin Stem. 



1. Cut cross and longitudinal sections of the stem of Ciuurbita pepo L., 

 stain and mount, or study prepared slides. Sketch the cross section under dis- 

 secting microscope. Note the epidermis, the cortex, the vascular bundles, the 

 pith, and the large central cavity. 



2. Under high power study the longitudinal sections and draw sieve-tubes 

 showing the sieve-plates in the phloem. 



3. In the xylem find and draw one of the large reticulate wood vessels ; also 

 a spiral wood vessel with a single spiral thickening and one with two spirals ; 

 also draw an annular wood vessel in which the thickenings are in the form of 

 rings. 



XCIII. Dicotyl Woody Stem. 



1. Cut cross sections of linden twigs (7/7/d: sp.) preserved in alcohol. Take 

 one very young branch, one a year old, one two years old, and one three years 

 old. Mount and stain ; or use prepared slides. Study under low and under 

 high power. 



"2. Make a series of diagrams showing the primary structure and how the 

 secondary structures are developed for the first three years. 



3. Make a sketch of a cross section of a polished tree trunk of black walnut 

 {/uglans nigra L.), showing these structures : pith, heartwood (duramen), sap- 

 wood (alburnum), annual rings with spring and fall wood, medullary rays, the 

 stelar cambium and phloem (mner bark) separated by irregular strips or arcs 

 of corky tissue from the outer bark. The outer bark has been developed from 

 the cortex and phloem and modified by successive layers of cork cambiums 

 (phellogen). These irregular strips of corky tissue can easily be seen in the 

 outer bark with the naked eye. 



4. Compare with the walnut a polished section of the trunk of a bur oak 

 (^Quercus tfiacrocarpa Mx.). In this the medullary rays are much more promi- 

 nent. 



XCIV. The Root. 



(a) Section of Buckeye Root. 



1, Cut cross sections of one of the larger fleshy rootlets of Aesculus sp. 

 (preserved in alcohol). Mount and draw under low power, representing the fol- 

 lowing structures : the four or more primary xylem bundles, four or more primary 



