14i Principles of Plant Culture. 



232. Mulching tends to Prevent Drought, by inter- 

 posing a layer of poor-conducting material between the 

 ground and the sun's rays. This keeps the surface soil 

 cooler and so checks evaporation. 



The best mulching material is the one that conducts 

 both heat and moisture slowest. Straw, marsh hay, 

 leaves, manure, shavings, sawdust, spent tan, and sand 

 are all useful for mulching, but the first four named 

 are generally preferable to the others, especially if free 

 from weed seeds. 



Growing plants tend to dry the soil because the root- 

 hairs continually draw in soil water and force it into 

 the leaves (101) where it passes off by transpiration 

 (74). Weeds, therefore, rob crops of moisture (336). 



233. Irrigation, i. e., the extensive watering of out- 

 door plants, is the final remedy for drought. It is nec- 

 essary to plant culture in arid regions, and may be 

 profitably employed at certain times in the great ma- 

 jority of seasons in many localities where the annual 

 rainfall would satisfy the needs of crops, were it more 

 uniformly distributed. 



234. Drying beyond a certain limit Kills Plant Tis- 

 sues by destroying in part their power for conducting 

 water. Care should be used to retain the normal moist- 

 ure in buds (394), cuttings (358), and cions (386) and 

 in the roots of plants lifted for transplanting. 



