REPRODUCTION 



359 



length, the tip being turned upward and left uncovered. The 

 covered section in time will produce adventitious roots after which 

 the branch may be cut off and the layer separated from the mater- 

 nal plant (Fig. 147). Sometimes rooting does not occur under 

 such procedure. Then it is necessary either to make incisions on 

 the part of the branch that is covered with earth, or to girdle it. 

 A callus is usually formed above the 

 incision or girdle, from which roots 

 will arise. 



Cuttings usually consist of a sec- 

 tion of the stem, either with or with- 

 out leaves. Before being used their 

 lower ends are dug into the earth to a 

 certain depth. The soil used for this 

 purpose must be very loose, preferably 

 sand, and the cuttings have to be 

 placed in an inclined position, so that 

 their lower end should not be too deep 

 in the soil. This is necessary, owing 

 to the fact that the healing of the 

 wound caused by the cutting and the 

 subsequent formation of roots leads 

 to an intensive respiration, therefore, 

 a liberal access of air is indispensable 



A high humidity is another necessary oht fZ* * ^ W ^ * 



Fig. 147. — Showing a method of 

 i layer (b) from 

 grapevine (after Molisch). 



factor for successful rooting. This 

 prevents the cuttings from drying before they have had time to 

 develop their own root system. This is particularly essential for 

 cuttings that bear leaves. Hence, previous to rooting, cuttings 

 are often kept in greenhouses or in special boxes with glass lids, 

 or they are placed under glass frames. Some cuttings, as those 

 of willow, root very readily within a few days, while others, such 

 as conifers, or camelias, require several weeks or even months. 



Cuttings also may be obtained from the roots of certain plants. 

 These are dug completely into the earth, in a somewhat inclined 

 position. Adventitious buds will then be formed on their upper 

 section, which will produce shoots, while the roots will be formed 

 from the lower section. 



A leaf also may be used as a cutting. It is planted with its 

 peduncle into moist soil. In most instances this will result in 



