PATH OF LEAF-MADE FOOD DOWN THE STEM 4] 
Starch is an insoluble substance, and so cannot pass through 
the cell walls. It therefore changes into a soluble sugar 
before being conveyed away, and on reaching its destination 
may remain as sugar, as in the beet-root, or be changed 
again into starch, as in the potato tuber. In connection 
with this explanation simple experiments should be made 
shewing— 
(a) The insolubility of starch ; 
(b) The solubility of sugar ; 
(c) The presence of starch in the potato tuber ; 
(d) The presence of sugar in the beet-root. 
Culture Solutions. The food of plants consists of 
the following substances (a) organic: oxygen, hydrogen, 
nitrogen, carbon; (b) inorganic: potash, magnesia, lime, 
phosphoric acid, sulphuric acid, iron, silica, soda, chlorine. 
Of these the whole of the organic substances and the first 
six of the inorganic substances are essential ; plants cannot 
grow without them. ‘The last three, though not essential, 
are found in many plants. , 
If the plant be supplied with those substances which are 
essential, it will grow and thrive ; if these be withheld from 
it, it will die. Interesting experiments can be made by 
growing plants in water or sand to which plant food has 
been supplied, these substances in themselves containing 
little or no available plant food. 
In each of two pots filled with sand, place a few bean or 
pea-seeds. Moisten these every few days, the one with 
pure water, and the other with a small quantity of some 
culture solution. The seeds in the pot on which the water 
is poured, will germinate and continue to grow until the 
supply of food contained in the cotyledons is exhausted, 
and may reach eight or nine inches above the edge of the 
pot. Those in the other pot supplied with all the essential 
substances will grow into large plants, and if the conditions 
be favourable, may bear flowers and fruit, | | 
