CHAPTER I 



The sieve tubes seen in longitudinal section are observed to be very 

 elongated vessels, with perforated partition walls at intervals in their 

 length ; the vessels are continuous throughout their length. 



In the internodes the fibro-vascular bundles run parallel, but at the nodes 

 they freely branch and communicate with each other, and pass on into the 

 leafbud and next intemode, descending right into the roots of the cane. 



Function of the Stalk. — The stalk serves in the economy of the plant in 

 three ways. First of all, as a mechanical structure it supports the leaves 

 and inflorescence ; secondly, the fibrovascular system is charged with the 

 duty of transporting water and food material from the roots to the leaves 

 and carrjdng back to the stem the products of metabolic change formed 

 in the leaf ; thirdly, the parenchymatous cells receive the material so 

 elaborated, which is there stored, or else used up as a source of energy by 

 the growing plant. 



Physiology of the Stalk. — In the life history of the stalk the following 

 phases are distinguished : — 



1. In very young parts of the stalk only 

 starch or albumen is present, which is con- 

 sumed little by little in the formation of 

 cellulose. 



2. In young, rapidly growing parts of 

 the stalk, the cane sugar brought down by 

 the leaf is inverted, and whereas in the 

 leaf the proportions of sucrose, glucose, 

 and fructose were as 4 : 2 : i, in the young 

 joints the proportions are o • 8 : i : i. A part 

 of the invert sugar is used up in the for- 

 mation of fibre, a part unites with the 

 amides to form albumen, and a part is 

 deposited as starch. In consequence of the 

 inversion, the osmotic pressure is raised and 

 this tends to favour the absorption of plant 

 food. 



3. In older joints the sucrose formed in 

 the leaf remains unchanged when it reaches 



the joint, and the reducing sugars are used up, partly in respiration, or, 

 perhaps, are partly converted by a reverted enzyme action into sucrose. 



4. When the stalks are developed, the accumiilated invert sugar is 

 converted into sucrose ; of the reducing sugars remaining the glucose is 

 generally in excess. 



5. When the stalks are ripe the leaves die and the accumulation of 

 sugar gradually ceases ; the remainder of the reducing sugars is changed 

 to sucrose, eventually only traces remaining. 



6. When the stalks are over- ripe the sucrose in the older joints is partly 

 inverted, but this change does not prevent the younger parts of the cane 

 accumulating sugar. 



The Leaf. — The leaves of the cane are alternate and opposite, one at 

 each joint ; actually, the leaf consists of two paits, the leaf sheath and the 

 leaf blade. The leaf sheath springs from the node. It completely embraces, 

 at its base, the stalk, and gradually recedes from it ; the sheath is colourless 



Fig. 3 



