PRINCIPLES OF PLANTING AND CULTIVATION 53 



under the row of plants to be watered. The openings at the joints, 

 as well as the porous nature of the tile, allow the water to escape 

 into the soil. The precaution to be taken in the installation of this 

 system is careful grading of the lines of pipe so as to insure 

 an equal distribution of the moisture. A plan for subirrigating 

 greenhouse beds is described and illustrated in figure 26, page 80. 

 The grower can ill afford to overlook or neglect any factor of 

 crop production which increases his risk. The relative importance 

 of factors of safety, such as cold frames, muslin-covered frames, 

 fertilizers, irrigation, insecticides, and fungicides, will vary with the 

 crop and locality. In one section frost protection will be the con- 

 trolling factor, in another water, and in still another protection 

 from disease may be the measure of success. The wise grower will 

 soon determine the limiting factor for each crop in his locality. 



