Drainage deepens the Soil, and gives the roots a larger pasture.--Cobbett's Lucerne 30 feet deep.--Mechi's Parsnips 13 feet long!--Drainage promotes Pulverization.--Prevents Surface-Washing.--Lengthens the Season.--Prevents Freezing out.--Dispenses with Open Ditches.--Saves 25 per cent. of Labor.--Promotes absorption of Fertilizing Substances from the Air.--Supplies Air to the Roots.--Drains run before Rain; so do some Springs.--Drainage warms the Soil.--Corn sprouts at 55 deg.; Rye on Ice.--Cold from Evaporation.--Heat will not pass downward in Water.--Count Rumford's Experiments with Hot Water on Ice.--Aeration of Soil by Drains. CHAPTER XIV. DRAINAGE ADAPTS THE SOIL TO GERMINATION AND VEGETATION. Process of Germination.--Two Classes of Pores in Soils, illustrated by cuts.--Too much Water excludes Air, reduces Temperature.--How much Air the Soil Contains.--Drainage Improves the Quality of Crops.--Drainage prevents Drought.--Drained Soils hold most Water.--Allow Roots to go Deep.--Various Facts. CHAPTER XV. TEMPERATURE AS AFFECTED BY DRAINAGE. Drainage Warms the Soil in Spring.--Heat cannot go down in Wet Land.--Drainage causes greater Deposit of Dew in Summer.--Dew warms Plants in Night, Cools them in the Morning Sun.--Drainage varies Temperature by Lessening Evaporation.--What is Evaporation.--How it produces Cold.--Drained Land Freezes Deepest, but Thaws Soonest, and the Reasons. CHAPTER XVI. POWER OF SOILS TO ABSORB AND RETAIN MOISTURE. Why does not Drainage make the Land too Dry?--Adhesive Attraction.--The Finest Soils exert most Attraction.--How much Water different Soils hold by Attraction.--Capillary Attraction, illustrated.--Power to Imbibe Moisture from the Air.--Weight Absorbed by 1,000 lbs. in 12 Hours.--Dew, Cause of.--Dew Point.--Cause of Frost.--Why Covering Plants Protects from Frost.--Dew Imparts Warmth.--Idea that the Moon Promotes Putrefaction.--Quantity of Dew. CHAPTER XVII. INJURY OF LAND BY DRAINAGE. Most Land cannot be Over-drained.--Nature a Deep drainer.--Over-draining of Peaty Soils.--Lincolnshire Fens. Visit to them in 1857.--56 Bushels of Wheat to the Acre.--Wet Meadows Subside by Drainage.--Conclusions. CHAPTER XVIII. OBSTRUCTION OF DRAINS. Tiles will fill up, unless well laid.--Obstruction by Sand or Silt.--Obstructions at the Outlet from Frogs, Moles, Action of Frost, and Cattle.--Obstruction by Roots.--Willow, Ash, &c., Trees capricious.--Roots enter Perennial Streams.--Obstruction by Mangold Wurtzel.--Obstruction by Per-Oxide of Iron.--How Prevented.--Obstructions by the Joints Filling.--No Danger with Two-Inch Pipes.--Water through the Pores.--Collars.--How to Detect Obstructions. CHAPTER XIX. DRAINAGE OF STIFF CLAYS.