CELL-CONTENTS AND CELL-WALLS. 63 



an hour test some of the liquid with Fehling ; no sugar is 

 present, the action of the diastase having been arrested by 

 the low temperature. Now keep the tube at 40 C. for 

 ten minutes ; the paste becomes clear and will soon reduce 

 Fehling, showing that the enzyme has not been destroyed 

 by the cold to which it has been exposed. 



(i) That maltose is the form of reducing sugar produced by the 

 action of saliva or of malt extract can be proved. To starch solution 

 add some saliva or malt, keep at 40 C., and at intervals of two 

 minutes take out a drop or two of the liquid with a glass rod, place 

 it in a white saucer, add iodine, and note the colours given indi- 

 cating the stages between starch and maltose. At first, blue (soluble 

 starch) ; then violet (a mixture of red due to dextrin and blue to 

 starch) ; then reddish-brown (dextrin alone) ; then yellowish brown, 

 and finally no reaction at all (dextrin mixed with maltose). Now 

 test a portion with Fehling (this might be done with the successive 

 stages if the experiment is made in a large tube with plenty of 

 material), which will prove the presence of a reducing sugar. After 

 the liquid has ceased to give any iodine reaction, add to it alcohol, 

 which precipitates the dextrin ; filter, and test the filtrate for 

 maltose ( 66), which is not precipitated by the alcohol. 



74. Translocatiou of Starch in Feas and Beans. 



(a) Cut transverse sections of a cotyledon of Bean or Pea ; 

 treat some with iodine. Note that the cotyledon is made 

 up of (1) a layer of small-celled epidermis; (2) the 

 general parenchyma, consisting of larger cells separated 

 by intercellular air-spaces ; (3) the veins, appearing as 

 patches and streaks of small-celled tissue. The cells of 

 the parenchyma contain large starch grains and much 

 smaller protein grains, but these are absent from the 

 epidermis and veins. Test sections for sugar with Feh- 

 ling's solution. 



(6) Cut sections of the radicle and plumule, and of the 

 young foliage-leaves (detach some of these and mount 

 them entire), and note that the cells contain little or no 

 starch in the resting seed. Test sections with Fehling; 

 no sugar (or only a trace) is present. 



(c) Now examine seedlings, treating sections with iodine, 

 and note that when the root is about 5 cm. long numerous 

 starch grains appear in the cortex and pith of the root and 



