THE CAXE 



due to the development or absence of colouring matter in streaks running 

 lengthwise with the stalk. Thus with a diminution of chlorophyll in stripes 

 in a yellow cane, a green and yellow ribbon cane results ; similarly, green 

 and red, and \-ellow and red canes are known, and also varieties striped 

 in two shades of red. The last case may occur in a cane with an even dis- 

 tribution of the red colouring matter, anthocyan, overl3ing strips of chloro- 

 phyll the colour of which is masked. Perhaps all arrangements possible 

 from ever3' combination of the three colours may occur. From striped 

 canes self-coloured sports frequently occur, and this subject, which is of 

 considerable economic interest, is discussed more full}' 

 in Chapter IV. 



Structure of the Stalk. — On cutting across a cane 

 it will be seen that it consists roughly of three parts, 

 a hard outer rind, and a mass of softer tissue in the 

 interior, interspersed with fibres, the latter being 

 more frequent about the peripherv^ of the stalk. The 

 rind is made up of a thick epidermis with a strong 

 outer cuticle, often with a thick layer of wax outside, 

 imper\ious to water, and a layer of thick-walled cells ; 

 the function of the cuticle is to prevent evaporation 

 of water from the stem of the cane, and to protect the 

 softer interior parts from mechanical injuries ; the 

 layer of thick-walled cells gives rigidity and strength 

 to the stem. These thick-walled cells graduall}- pass 

 into the thin-walled cells of the ground tissue, or 

 parench\Tna, which serve to store up the sweet juice 

 of the cane. The fibres are known as the fibro- 

 vascular brmdles ; they consist of the wood vessels, 

 sieve tubes and companion cells, surroimded by thick- 

 walled fibres. 



A cross-section of the cane, after Cobb^, as seen 

 under the low power of a microscope, is shown in 

 Fig. 2. It consists of : — i. The epidermis, ^vith thick 

 cuticularized walls. 2. Thick- walled ground tissue of 

 the rind. 3. A small vascular bimdle ; these are 

 found mainl}^ in the outer portion of the stem, and 

 their function is chiefl}' mechanical. 4. An inter- 

 mediate bundle with two vessels and a few thin-walled 

 phloem elements. 5. Thick- walled fibres ; these are 

 the mechanical elements of the bundles, and are 

 more numerous in the bundles towards the outside. 

 6. Thin-walled cells of the ground tissue or paren- 

 chjTna. 7. A large vascular bundle found tow^ard 

 stem. 



In Fig. 3 is shown more highl\' magnified a bundle corresponding to 7 

 in Fig. 2. I is a vessel with unbordered pits ; 2, an annular vessel ; 3, a 

 sieve tube with the companion elements making up the phloem ; 4, an 

 intercellular air space ; 5 and 7, thick-walled mechanical elements, the 

 fibres, or sclerenchjTna, forming a sheath aroiuid the bundle ; and 6, ground 

 tissue or parench\-ma. ^^^len seen in longitudinal section the cells of the 

 parenchjTna are found to be rather longer than wide. 



Fig. 2 



the centre of the 



