42 STKUCTURE AND PHYSIOLOGY OF SEED PLANTS 



28. Minute structure of the climbing dicotyledonous stem.* * 



A. Study, first with l.p. and then with m.j)., thin cross sections 

 of clematis stem^ cut before the end of the first season's 

 growth. Sketch tlie whole section without much detail, and 

 then make a detailed drawing of a sector running from cen- 

 ter to circumference and just wide enough to include one of 

 the large bundles. In general label these drawings, as in 

 Figs. 57 and 58 of the Principles. Note : 



1. The general outline of the section. 



2. The number and arrangement of the bundles. (How 

 many kinds of bundles are there ?) 



3. The comparative areas occupied by the woody part of 

 the bundle, and that which belongs to the bark. 



4. The way in which the pith and the outer bark are con- 

 nected (and the bundles separated) by the medullary rays. 



B. Examine a longitudinal section of the same kind of stem 

 to find out more accurately of what kinds of cells the pith, 

 the bundles, and the outer bark are built. Which portion 

 has cells that are nearly equal in shape, as seen in both 

 sections ? 



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

 Schenck, Karsten, 1. 



29. Kinds of cells which compose sterns.^ Examine with m.p. these prepara- 

 tions (A-J below). Study very carefully each of the required sections, find 

 in it the kind of cell referred to, and make a good drawing of a group of 

 cells of each kind. 



A. Very thin sections of the outside layers of the cortex of a potato, 

 some cut tangential to the outer surface, other sections cut at right 

 angles to it {cork). 



B. Thin sections of the green layer of the bark of Forsythia^ Evonymus, 

 or box elder {Negundo) {green cells of cortical parenchyma). 



C. Thin cross sections and lengthwise sections of the inner bark of 

 linden twigs. Test with phloroglucin {hard bast).^ 



1 Clematis virginiana is simpler in structure than some of the other woody 

 species. Aristolochia or Menispennum sections will do very well. If unmounted 

 sections are studied, stain with phloroolucin (Sec. 12, D). 2 gee also Sec. 138, B. 



s Both hard-bast fibers and wood fibers are known as sclerenchym,a, but they 

 differ somewhat in appearance and much in location. 



