THE HISTOLOGY OF THE CELL 



EXPT. 81. Sow a few mustard seeds in two plant pots ; keep the 

 soil moist ; place one in a dark place and the other in a light place. 

 Observe from day to day. Note 



The stems and leaves of those plants kept in the dark are far longer 

 than those grown in the light, but they are pale yellow or dirty white in 

 colour. 



Those grown in the light are bright 

 green. Light is necessary for the de- 

 velopment of chlorophyll, 



EXPT. 82. Obtain a few young 

 Potatoes and cut them into slices. Place 

 them in a weak solution of picric acid 

 for a day or two. Wash the solution 

 out with a weak solution of alcohol, and 

 harden the slices in a 70 per cent, solu- 

 tion of alcohol. Cut sections from near 

 the surface, and stain them in alcohol 

 and iodine solution. Mount in glycerine, 

 and examine under a high power. 

 Note 



(i) Some of the granules in the protoplasm stain blue. These are 

 starch grains. 



(ii) Attached to some of the starch grains small yellowish bodies may 

 be seen ; these are leucoplasts. 



Leucoplasts may be seen in colourless tissue in which starch 

 is being stored up. Underground tubers and rhizomes contain 

 them, 



Starch Grains. Chloroplasts in those cells which are 

 exposed to light always contain starch grains. In many 

 cases the starch grain is so large "that the chloroplast only 



FIG. 109. Cells from prothallus 

 of Fern. (20.) 



FIG. no. Starch grains of Wheat. 

 A, large ; B, small grains. 

 (X 54 o.) (S.) 



6 



FIG. in. Starch grains of' Oat?. 

 A, compound grains ; B, isolated 

 grains. (X540.) (S.) 



surrounds it as a thin covering. Chloroplasts are always form- 

 ing starch at the expense of the sugar which is produced by 

 the constructive activity of the chlorophyll and the protoplasm. 

 In the green parts of plants starch grains are very small because 



