64 MULTIPLICATION OF PLANTS. 



in producing these roots by placing in a properly moist situation, 

 a branch in which the progress of the descending sap is slow, 

 therefore permitting an accumulation of nutritive matter in it. 

 To arrest in this way the descending sap at a point from which 

 we wish to produce adventitious roots, we sometimes make a cir- 

 cular incision through the thickness of the bark, and place in it 

 a tightly drawn ligature, and then surround it with moist earth ; 

 sometimes we simply bend a branch into the ground, because, at 

 t'le point where it is bent, the nutritive juices, being forced to 

 overcome their own weight in order to ascend towards the stem, 

 are retarded in their progress ; at other times we take advantage 

 of natural knots that exist in a branch and favdur the development 

 of adventitious roots ; and there are some plants, the branches 

 of which, when surrounded by moist earth or moss, put forth 

 roots without a stagnation of the nutritious juices being necessary. 

 When the roots appear, we cut the branch so as to separate it 

 from the plant to which it belonged, and it then constitutes a new 

 individual. 



5. But we do not separate the slip or branch until the roots 

 are formed, that is, when it possesses all the parts that compose 

 a complete plant ; but it often happens that a branch cut before 

 it has put forth adventitious roots, continues to vegetate and pro- 

 duce roots so as to constitute a new individual : for example, a 

 branch of willow freshly cut and planted in moist earth, promptly 

 takes root and becomes a tree similar to that from which it 

 was detached ; it is then called a slip or sucker. All plants 

 may be multiplied in this way, but with more or less facility ; as 

 this operation rarely succeeds, gardeners seldom have recourse 

 to it. 



6. It is not the branches alone that may give rise to adventi- 

 tious roots and constitute a slip or shoot ; sometimes the leaves 

 will perform this office ; for example, the leaves of the orange, 

 of the fig, &c., detached from their stems and fixed in the earth 

 by their petiole, will take root by their principal nerve, and after- 

 wards give rise, from the superior surface of their paren'chyma, 

 to ascending stems. 



7. The multiplication of plants by grafting, of which we 

 have already spoken, is also a mode of propagation that belongs 

 to this class of phenomena, because it is effected by simple divi- 

 sion ; only the part of the plant which is separated, instead of 



5. When is the new branch separated ? 



6. Do any other parts than branches produce adventitious roots ? (See 

 page 19.) 



7 What is the multiplication of plants by grafting ? 



