WORK OF THE SHOOT 91 



of stem about the thickness of a lead pencil and cut several 

 slices across it. Lay them on a glass slip and place on them 

 a drop of iodine solution. By means of a pocket lens 

 examine the surface and note the effect of the stain. 

 Compare the yellow-brown walls of the wood with those 

 of the medullary rays and with the outer cells of the pith. 

 These are crowded with dark purple-stained starch grains. 



CHAPTER VIII 



WORK OF THE SHOOT {Continued) 



Transpiration. It is a matter of common observation 

 that, when plants are grown under a bell-jar or in a glazed 

 case, the sides of the chamber are covered with drops of 

 water. Where has this water come from ? Has it come 

 from the soil or from the shoots ? If from the latter, 

 seeing that a plant is provided in its roots with so excellent 

 a means of obtaining water, why should so much be thrown 

 off by its shoots ? 



A simple experiment will enable us to decide the matter. 

 Plant in a pot a single rosette of London Pride, take a piece 

 of lead-foil large enough to cover the top of the pot, cut it 

 from one side to the centre, bring the two cut edges round 

 the stem beneath the leaves and fold them closely over, 

 pressing the sides around the pot so as to exclude all 

 moisture from the soil (Fig. 55). Take a small vessel, 

 fill it with dry calcium chloride (a substance which 

 readily absorbs water), and weigh it carefully; place this 

 on the top of the lead-foil alongside the plant, and cover 

 the whole with a bell-jar, sealing the edge with vaseline. 

 Allow this to remain for a day ; then examine. Remove 

 the bell-jar and note what change has taken place in the 



