ioo PRACTICAL BOTANY 



LEAF 



Note that the phyllotaxis in the Maize is | : the leaf is sessile, 

 and sheathing in its lower half, with a ligule at the upper limit 

 of the sheath ; the form of the lamina is lanceolate, margin 

 entire, ciliate, midrib well marked ; venation parallel ; upper 

 surface hirsute ; lower glabrous. 



I. Treat a piece of the thin peripheral part of a leaf (which 

 has been previously bleached in alcohol) with potash till it is 

 transparent ; mount in glycerine, and examine under a low 

 power. Observe 



1. The parallel course of the vascular bundles. 



2. Their frequent lateral fusion, by means of small branch- 

 bundles. 



3. The absence of stomata above the vascular bundles, and 

 their arrangement in rows in the spaces between them. 



4. The various forms of hair - t and especially the conical uni- 

 cellular hairs, which give the ciliate character to the margin of 

 the leaf. 



II. Cut transverse sections of the lamina ; mount in water, or 

 dilute glycerine. Other sections may be treated with alcohol to 

 expel the air-bubbles ; the chlorophyll will, at the same time, be 

 dissolved out : other sections may be mounted in chlor-zinc- 

 iodine, and kept for comparison with the above. Examine with 

 a low power. 



The section presents a sinuous outline, corresponding to a 

 certain extent to the arrangement of the main vascular bundles : 

 at the midrib the section widens out. Note the following 

 arrangement of tissues : 



I. Covering both surfaces of the leaf is an epidermis, re- 

 sembling that of the stem, but bearing hairs of various form, 

 mostly simple, conical : the largest of them are surrounded at 

 the base by an outgrowth of the neighbouring epidermal cells. 



Note the stomata on both surfaces, with small guard-cells, 

 surrounded by two subsidiary cells : these will be further 

 examined below. 



