622 HORTICULTURE, FORESTRY, FLORICULTURE 



they should be practically water-tight. With wooden benches it is 

 desirable that the supports should be close enough to prevent the 

 sagging of the boards. The bottoms were formerly made of clear, 

 matched lumber, laid in white lead, but for several years ordinary 

 barn boards free from loose knots have been used at the Michigan 

 Station. If these are laid close together and firmly nailed to the 

 stringers to prevent their humping, they will, when wet, swell suf- 

 ficiently to close the cracks. The writer generally lays the boards 

 across the beds upon stringers running lengthwise of the house. To 

 close the remaining cracks and to preserve the lumber it is well to 

 coat the inside of the bed with a cement made of one part of water 

 lime and three of sharp sand. This should be made into a thick 

 paste and spread over the surface about one-fourth of an inch thick. 

 For a bed with tile or slate bottoms a similar covering will render 

 them sufficiently tight (fig. 52). 



In case a solid bed is used, a tight bottom about 8 inches below 

 the intended level of the bed is necessary. If the subsoil is stiff 

 clay, it may be puddled and will then hold water, but it will generally 

 be better to spread an inch or so of gravel and, after thoroughly 

 ramming it, to place over the surface three-fourths of an inch of 

 cement prepared as above. The beds should have sides of the same 

 material 3 inches high. 



The best way of distributing the water is by means of 2^-inch 

 drain tiles, placed either lengthwise or across the beds at intervals 

 of 3 or 4 feet. If the line is not over 50 feet in length, they may be 

 placed upon a level, but for greater lengths the line should have a 

 slope of 1 or 2 inches in 50 feet. To learn if the water is circulat- 

 ing properly, it is well to make an opening into the tiles once in 

 20 feet, into which a small flowerpot can be set. In laying the tiles 

 care should be taken that the cracks between them are of an even 

 size. As a rule, it will be found that they have become slightly 

 curved in baking, so that the ends are not square, and if the convex 

 sides are placed uppermost there will be a small opening at the under 

 side large enough to allow the water to escape freely. If thought de- 

 sirable, several lines of tile can be so connected at one end that they 

 may all be filled from one hose, or faucets may be arranged so as 

 to supply water in any desired amount to the different lines. The 

 water can be admitted through sewer-pipe elbows, or by raising the 

 end of the last tile so that it will show above the surface. 



One-inch gas pipes with one-fourth-inch holes every foot have 

 also been tried at the Michigan Station. While good results were 

 obtained, the openings frequently became clogged and the water 

 was not given off as freely as when tiles were used, so that a longer 

 time was required to water the beds. Besides being cheaper the use 

 of tiles seems in every way preferable. 



In a general way subirrigation in greenhouses shows about the 

 same advantages over surface irrigation as are found in the garden, 

 but while the saving in time of watering and in the amount of water 

 required is even greater in proportion, the direct benefits, especially 



