^/ 



10 MANUAL FOR SUGAR GROWERS. 



thus pass through the membrane ; they are distin- 

 guished as crystalloids. Notv crystalline substances 

 like gelatine, albumen, etc., cannot pass through, 

 and are known as colloids. In the root the cells 

 are the bladders, but mth the solution of plant-food 

 outside them; this is continually passing into the 

 cells ; the solution inside the cells is prevented from 

 becoming of the same strength as that on the out- 

 side, owing to the transfer of the plant-food by fur- 

 ther osmose into other cells, till it is finally used in 

 the process of growth. 



The Leaf. — The leaf of the sugar-cane is about four 

 feet long and two inches wide, tapering to a point ; the 

 leaf -stalk is developed into a sheath which closely 

 embraces the stem. In internal structure the leaf is 

 somewhat complicated ; the upper and under sm'faces 

 are covered with a skin or tissue called the epider- 

 mis, which is composed of thin- walled flat cells hav- 

 ing coloui'less contents ; between the upper and under 

 epidermis is a mass of tissue the cells of which are 

 filled with green contents ; running from end to end 

 of the leaf are veins which are continuations of the 

 fibro- vascular bundles of the stem. It will be seen in 

 the drawing (Fig. 4) that these cells having green- 

 coloured contents are not packed closely together, 

 but that there are air-spaces between them, these 

 air-spaces being very large in some places ; it will be 

 noticed, too, that these air-spaces are in connection 

 with the outer air by means of openings through the 

 epidermis. If a little of the epidermis be stripped 

 off and examined with the microscope, these open- 

 ings may be readily distinguished ; the epidermis is 



