108 



VIII. THE MONOCOTYLEDONOUS STEM. 



Do not be satisfied with a single section, as otherwise the chance 

 of obtaining in the preparation a vascular bundle cut, as it must 

 be, actually median is small. Such a median-cut vascular bundle 

 can be recognised on examination of the section, in that it will 

 show at the same time the intercellular passage, the spiral or 

 annular vessels, and the bast. If the section is laid in chlorzinc 

 iodine we shall note the violet coloration of the bast, and the 



* 



*:</ 







FIG. 41. Longitudinal radial section through a vascular bundle in the stem otZea 

 Mais, a and ', segments of an annular vessel ; sp, spiral vessel ; v, sievetube ; 

 s, companion-cells ; cj>, protophloem ; /, air passage (intercellular passage) ; vq, sheath 

 ( x 180). 



thin- walled cells surrounding the intercellular passage have also 

 a violet tone. The other elements, in accord with what we have 

 seen in the cross-section, are coloured yellow to yellowish-brown. 

 For further study we preferably select a section which we have 

 stained with soda-corallin (Fig. 41). It is desirable first of all 

 to determine in which direction in the section the surface of the 

 stem lies. As in the cross-section, our examination will proceed 



at a couple of points near the middle, and about 1 inch apart, bend the ends 

 down, using them as a handle to hold the material by, and take the sections 

 then from the short median piece. [Eo.] 



