SCALE-LIKE LEAVES 313 



Sometimes the leaves are small and scale-like, though 

 still green (cypress), and in such cases the stem as well 

 as the leaves may have a well-developed photosynthetic 

 tissue. Finally, the leaves may be reduced to minute 

 functionless scales, photosynthesis and transpiration 

 being carried out entirely by the green stem, to which 

 the photosynthetic tissue, resembling in all respects 

 the mesophyll of a typical leaf, is then confined. 



Occasionally in such cases the leaves are represented 

 by bristles or spines instead of scales. 



PRACTICAL WORK. 



(1) Make a clean cut under water across the base of the leaf 

 stalk of a geranium (Pelargonium) leaf, and place it in a glass 

 with the cut end dipping below the surface of aqueous eosin 

 solution. After a time observe that the eosin has been sucked up 

 the xylems of the vascular bundles and eventually appears in 

 the leaf veins. 



(2) Examine in a drop of dilute glycerine the transverse section 

 of the typical dorsiventral leaf blade (Hellebore) provided. Make 

 a drawing under the high power of (a) the midrib showing xylem, 

 phloem, fibres, collenchyma and epidermis, (b) of a typical segment 

 of the blade showing the upper epidermis with cuticle, palisade 

 cells, spongy tissue, with fewer chloroplasts and large intercellular 

 spaces, and the lower epidermis with a stoma in section. 



(3) To another section add a drop of Schulze's solution, and 

 note the different staining of the cuticle and of the wall substance 

 below it. 



(4) Strip off a piece of the epidermis from the surface of the 

 leaf of Iris, taking care that you get part of it at least free from 

 adherent mesophyll cells. Mount the strip in dilute glycerine 

 with the outer surface uppermost. Find and draw a stoma with 

 adjacent epidermal cells carefully under the high power. In 

 focussing down, the sides of the rectangular vestibule first come 

 into view, and below this the two guard cells with stomatal 

 pore between them. 



(5) Now examine a transverse section of the same leaf. Find 

 and draw very carefully a stoma, which is now seen in sectional 

 view. Note especially the cuticular thickenings of the sides of 



