202 Principles of Plant Culture. 



b A comparatively low air temperature is import- 

 ant in growing many plants from cuttings of the stein 

 (377), because it is essential that the stem growth be 

 held in check until roots are formed. A soil tempera- 

 ture 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 spe- 

 cial precautions, however, it is possible to propagate 

 many plants from cuttings during the warm season. 



a Abundant moisture is important in growing plants 

 from cuttings, because moisture favors root develop- 

 ment (88), and water is essential to cell growth (62). 

 The amount of water required varies considerably with 

 different plants and conditions. 



With cuttings containing leaf tissue (377, 382), 

 transpiration (74) must be reduced to the minimum 

 until roots are formed, because water cannot be taken 

 up freely without root-hairs (100). For such cuttings, 

 therefore, the air as well as the soil must be kept 

 abundantly moist (369), and the direct rays of the sun 

 must be intercepted by shading (235). 



363. Methods for Controlling Temperature. The 

 alternations of temperature in the open air are un- 

 favorable to the development of cuttings, though many 



