64 CELL-CONTENTS AND CELL-WALLS. 



hypocotyl. Test sections of these with Fehling : sugar is 

 now present. As germination proceeds, starch disappears 

 (being replaced by sugar) from the older and fully elon- 

 gated tissues remaining, however, in the starch- sheath 

 around the ring of vascular bundles and appears in the 

 younger tissues. When the two primary foliage- leaves of 

 Phaseolus emerge they contain starch, but as they develop 

 it disappears from them, and by this time the amount of 

 starch in the cotyledons has become greatly reduced as 

 can be seen by testing sections (note that the starch grains 

 show extensive corrosion, with cracks and cavities). 



(d) Remove the coats from seedlings of Peas or Beans 

 in which the radicle has grown about 5 cm., grind or pound 

 up the seedlings with water, and filter. Put starch paste 

 into three saucers ; into A pour some of the filtered extract 

 from the seedlings, into B some extract that has been 

 boiled, and leave C as a control. After the three have 

 been in a fairly warm place for an hour or two, note that 

 a sample of the liquid from A gives only a reddish colour 

 with iodine, and ultimately remains uncoloured ; while B 

 and G become blue on adding iodine the diastase in B has 

 been destroyed by boiling. Transfer some of A to a test- 

 tube, and apply Fehling's test; note the abundant sugar. 



75. Translocatiou of Starch in Wheat. (a) Cut 

 and examine transverse and longitudinal sections of 

 a Wheat grain softened in water for an hour. Note 

 (1) the coat, consisting of a distinct epidermis, about two 

 layers of thick-walled cells, a layer of large flattened cells, 

 and then several layers of cells with more or less com- 

 pletely obliterated cavities these tissues, starting from 

 the outside, are derived from the ovary-wall (pericarp^, 

 the integuments (testa}, and the nucellus (perisperm) of 

 the ovule ; (2) the aleurone layer, or outermost layer 

 of the endosperm, consisting of cubical cells containing 

 abundant protein grains but no starch ; (3) the starchy 

 endosperm tissue, consisting of polygonal cells with 

 crowded starch grains ; (4) the embryo. To see the 

 successive layers of the grain coat more distinctly, mount 

 sections in potash. 



