204 PRINCIPLES OF PLANT CULTURE 



organic matter, as decaying material in the sand favors 

 the development of cutting-bench trouble. The same 

 sand should be used for but one lot of cuttings, as 

 a rule, for it is liable to become infested with fungi that 

 may work havoc with cuttings placed in it. 



369. Methods of controlling humidity. — Where mois- 

 ture needs to be controlled with especial care, as in 

 propagating delicate plants from green cuttings, or in 

 herbaceous grafting (393), the planted cuttings or the 

 grafted plants are often covered with bell-jars. To 

 guard against sudden fluctuations in temperature, a 

 larger bell-jar is sometimes placed over a smaller one. 

 By means of a bell-jar with a tight-fitting ground 

 plate, evaporation may be wholly prevented from cut- 

 tings or plants, if desired. Propagating-beds are often 

 covered with glazed sash, in addition to the glass roof 

 of the house, to assist in maintaining a moist atmosphere 

 about the cuttings (Fig. 99). 



370. Propagation by cuttings from dormant plants. — 

 For convenience, we separate propagation by cuttings 

 into two divisions, viz., propagation by cuttings from dor- 

 mant and from active plants. The requirements of these 

 two classes differ in some respects. 



We have seen that plant processes may not be wholly 

 suspended during the dormant period (176). This is 

 true not only of the plant as a whole, but also of detached 

 parts of the plant, if they are protected from evaporation. 

 If cuttings are taken from a plant in autumn and stored 

 during winter in a moist place of moderate temperature, 

 the cut surfaces will partially callus over (72), and the 

 formation of roots or buds may commence before spring. 



When new growing points must be developed before 

 the cuttings can form a plant, as with cuttings of the 



