"The earth is full of the goodness of the Lord."—Psalm xxxiii.
1185. Why do ripe fruits taste sweet, and unripe fruits taste sour?
Because the juices of the ripe fruit contain a large proportion of sugar, which in the unripe fruit has not been formed.
1186. Why do some leaves turn yellow?
Because they retain an excess of nitrogen. Leaves undergoing decay turn either yellow, red, crimson, or violet. Yellow is due to the excess of nitrogen; red and crimson to various proportions of oxygen; violet to a mixture of carbon; and green to chlorophyll.
1187. Why do leaves fall off in the autumn?
Because they have supplied for a season the natural wants of the tree. Every part has received nutrition through the spring and summer months; and the wants of the tree being supplied, the chief use of the leaf ceases, and it falls to the ground to decay, and enrich the soil.