ASEXUAL PROPAGATION OF PLANTS ON OWN ROOTS 57 



parts and filled with sand or other material. The moss or 

 sand must be kept moist by frequent watering until the 

 roots have developed. The use of this method is generally 

 confined to the greenhouse or situations where there is little 

 danger of the moss drying out. 



80. Time for layering. As a rule, spring is the best time 

 for layering, although sometimes it is performed in the fall. 

 Herbaceous plants of a succulent nature, such as geraniums, 

 can be layered in summer, when it is difficult to grow them 

 from cuttings. After layered plants have rooted, the new 

 individuals are cut off from the parent and set out, in some 

 instances in the fall, but in most cases in the following 

 spring. Some plants, however, such as the spirea, tajje two 

 years to root, from the time they are layered. 



81. Runners. Plants which, like the strawberry, produce 

 runners, are propagated by a sort of modified layer. From 

 the runners, new individuals are formed which may be cut off 

 and set out. Plants of this type are easy to propagate. 



82. Cuttings. Propagation by cuttings consists in re- 

 moving and planting certain portions of plants. Cuttings 

 may be made from leaf, stem, tuber, root, or bulb, the parts 

 most suitable differing with the species. A cutting must 

 contain living tissue and be able to multiply its cells; it 

 must have a growing bud or be able to produce one; and it 

 must contain enough stored food to keep up its life processes 

 while it is forming roots to enable it to take up food material 

 from the soil. Cuttings require, for their growth, moisture, 

 hfftt, oxygen, and light in amounts varying with the nature 

 of the plant, and must be placed in a suitable medium until 

 the roots develop. 



With most plants, the cuttings must go through a callus- 

 ing process before roots form. The callus is simply a growth 

 of cells formed from the normal growing tissue of the cutting. 

 In the hardwood cutting in Fig. 32, the callus will be seen as 

 a rim proceeding from the cambium layer at the cut surface. 



