Propagation by Cuttings. 193 



3(51. The Parts of plants to be Used for Cuttings, there- 

 fore, are preferably the younger, matured growths, since 

 the tissues of these are most vigorous; or else a part that 

 possesses a certain amount of healthy and vigorous leaf 

 tissue. .The cutting should always contain one or more 

 buds when practicable (128). 



362. Conditions that Favor the Growth of Cuttings. 



a A soil warmer than the air above it ( "bottom heat" ) 

 is important in growing many plants from cuttings. 

 Warmth stimulates plant growth, and when applied to 

 one part of a plant, it stimulates growth in that part. If 

 the soil about a planted cutting is warmed to a tempera- 

 ture considerably higher than that of the air above, the 

 growth of roots is stimulated. Indeed bottom heat often 

 excites growth in cuttings that will not grow without it. 



b A comparatively low air temperature is important in 

 growing many plants from cuttings of the stem (377), 

 because it is essential that the stem growth be held in 

 check until roots are formed. A soil temperature of 

 about 65 F., with an air temperature about fifteen 

 degrees lower, is suited to the great majority of plants 

 usually propagated under glass from cuttings. It is 

 important that these temperatures be maintained nearly 

 constant until roots have developed. 



Since we have better facilities for raising than for 

 lowering the natural temperature of the atmosphere, 

 propagation from cuttings is easiest at a time of the year 

 when the temperature of the atmosphere during the day 

 does not much exceed 50. By observing special pre- 

 cautions, however, it is possible to propagate many plants 

 from cuttings during the warm season. 



