310 PHYSIOLOGY OF NUTRITION. 



but the parenchyma of the active elongating secondary roots 

 contain much sugar. 



As the germination proceeds, the fat keeps disappearing more 

 and more completely from the endosperm as it finds employment 

 in the growth of the seedling. The hypocotyl straightens, and 

 the wood and bast of its vascular bundles undergo further develop- 

 ment. In proportion as the upper part of the hypocotyl elongates, 

 the starch and sugar derived from the fats also disappear from 

 the cells of the parenchyma. Starch grains are now to be detected 

 only in the starch sheath surrounding the fibro- vascular bundles. 



The function of the starch sheath will be more fully discussed 

 below ; it is sufficient here to point out its existence. It appears as 

 a closed sheath surrounding the circle of fibre-vascular bundles, 

 and, as shown in Fig. 112, is beautifully developed in the hypocotyl 

 of Ricinus. For further details we may consult Fig. 112. 



It may be stated generally that the development of the organs 

 of the embryo of Ricinus gradually progresses upwards from the 

 root through the hypocotyl to the cotyledons. With commencing 

 elongation and internal differentiation of the organs, large quan- 

 tities of starch appear in the cells of the parenchyma. When 

 elongation is rapidly advancing, much sugar is also to be found in 

 the parenchyma. But these carbohydrates disappear again from 

 the parenchyma when the elongation and development of the 

 organs is complete ; they have, in fact, been used up in the forma- 

 tion of cell substance. 1 



It has been stated that large quantities of starch are present in 

 the cortical and medullary tissue of the upper part of the hypocotyl 

 of Ricinus when it is still curved, and the cotyledons are still 

 imbedded in the endosperm. The quantity of starch is, as I found, 

 so large, that it is possible to demonstrate its presence macroscopi- 

 cally in lecture. For this purpose sections from the upper part 

 of the hypocotyl are treated on a slide with chloral hydrate, and 

 iodised Potassium iodide solution ; if the students hold the pre- 

 paration, covered by a cover-glass, to the light they can satisfy 

 themselves of the presence of large quantities of starch by the 

 blue coloration produced. 



In the germination of seeds of Raphanus sativus also a fair 

 quantity of starch appears. I found large quantities of starch in 

 the elongating hypocotyl of a seedling of this plant about four 

 days old, and grown at a temperature of 20 C. The root of the 

 seedling was very poor in starch. In the hypocotyl I found the 



