CHEMISTRT AND PHYSICS OF PLANTS 



85 



Practical Studies. — (as) Put a dry apple-twig into a short piece of 

 gas-pipe, closing tlie ends, not very tightly, with clay; 

 put it into a fire and heat to redness. The carbon 

 left will be of the form, and about half the weight, 

 of the dry twig. 



(J) Germinate several kernels of Indian corn in 

 moist sand, and when the roots are two to four cen- 

 timetres long transfer the plants to wide-mouthed 

 bottles or jars, supporting them as in Fig. 41. Fill 

 one of the jars with pure (distilled) water; fill a second 

 witli well-water (which always contains many, if not 

 all, of the materials of plant-food) ; fill a third with water 

 from a stream or pond (which also always contains all, 

 or nearly all, the materials of plant-food). Notice that 

 the plants will grow in all the jars, as all are supplied 

 with carbon dioxide and water, the most important 

 plant-food; but the best and longest-continued growth 

 takes place in the second and third jars. 



(c) In case the materials can be obtained, fill a fourth 

 jar (as in the previous experiment) with a solution of 

 the following constitution : 



Fio. 41.— 

 Showing meth- 

 od of maldiig 

 water - culture 

 experiments. 



Distilled water 1000 parts 



Phosphoric acid 0.13 



Lime 0.16 



Potash -0. 14 



Magnesia , 0. 02 



Sulphuric acid 0.03 



Nitric acid 0.46 



Chlorine 0. 001 



Sulphate of iron 0. 001 



With this solution perfect plants may be grown, if care be taken 

 to renew the solution from time to time. 



(d) Secure a quantity of Pond Scum (Spirogyra) in a dish of water; 

 expose it to the sunlight for some hours, and then examine it for 

 starcli witli the aid of the microscope, making use of the iodine test. 

 When starch has certainly been found, put the disli in a dark (but 

 not cool) chamber, and after some hours repeat the foregoing exami- 

 nation. No starch will now be found. 



(e) Select two thrifty potato-plants of about equal size and about 

 the period of flowering, when the tubers are beginning to grow; 

 cover one with a tight box or barrel, so as to shut oS all the light 



