ST OUMllfGS Ol' IMMATURE GEOWTHS. 35S 



and we aim to continue or accelerate the change, and not 

 to check it by onr operations. To accomplish this, it is 

 generally necessary to surround the cutting with a warm, 

 moist, and somewhat confined atmosphere, so that the 

 exhalation, which is very rapid in an open situation, can 

 be controlled. If the quantity of moisture given ofE by 

 the leaves is greater than that absorbed, then they will 

 surely droop, and artificial applications will be required 

 to revive them. 



Various devices are employed by propagators to secure 

 that peculiar state or condition of the atmosphere most 

 suitable to the growth of cuttings of different kinds of 

 plants.- Glass is the principal material used for covering 

 propagating houses, because it is the most durable, and 

 through it plants receive light, which is indispensable to 

 the giiowth of all those belonging to the higher orders ; 

 while, at the same time, heat and moisture are under the 

 control of the propagator. These houses may be made 

 of almost any size or form to suit the convenience or taste 

 of the owner, but those with a double pitch or span roof, 

 is shown in figure 53, are the most common, and probably 

 the most convenient for heating and ventilating, as well 

 as exposure to the light and direct rays of the sun during 

 the greater part of the day. 



The illustration on page 156 shows the interior per- 

 spective view of a section of a well-arranged propagating 

 house. It may be made of almost any desired length or 

 width, but eighteen or twenty feet is about the usual 

 width of a span-roof house of this kind. 



The side walls of the house may be of brick, stone, 

 concrete, or other durable material, and in very cold cli- 

 mates it is well to bank them up on the outside with 

 earth, and sod over the embankment. The house should 

 stand with ends north and south, although a slight devi- 

 ation from this direction will not be a serious objection. 

 The side walls should be low, not more than four or 



