CUEMISTRY AND PHYSICS OF PLANIS 85 
Practical Studies.—(a) Put a dry apple-twig into a short piece of 
gas-pipe, closing the 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. 
(0) 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 asecond 
with well-water (which always contains many, if not 
all, of the materials of plant-food); filla 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 pores 
with carbon dioxide and water, the most important (7 TT TRS 
plant-food; but the best and longest-continued growth 
takes place in the second and third jars. Fie. 41.— 
(c) In case the materials can be obtained, fill a fourth ml or eee 
jar (as in the previous experiment) with a solution of water -culture 
) 
the following constitution: SeReEeDeS 
Distilled water. wc asic sscwaecne van eevee besa 1000 parts 
Phosphoric acid............... SeUG ae esa ses eye 0.138“ 
LIMC xis seek bess oe as ese sate seiee) x 0.16“ 
POlASH: ss sevens armaragnamiigoeraainnes 64 eeiws daw 0.14 “ 
MAE NESTA: zcisci secs ahoemeiies ta as Ges gens eats 0.02 « 
SulphUriGaGid ae ois cs cas eae Ge ere nae memes 0.038 
Nittic ACId 6 nce auieae Rade es SERRE OTTO 0.46“ 
Chlorine: ssc cscseeasedtes soeweee ss seceeeee 0.001 ‘ 
Sulphate of iron.......... 0. cee eee eee a elarearwniie« 0.001 <* 
With this solution perfect plants may be grown, if care be taken 
to renew the solution from time to time. 
(ad) 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 
starch with the aid of the microscope, making use of the iodine test. 
When starch has certainly been found, put the dish 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 off all the light 
