24 f OKMATION OF ROOTS BY LEAVES. 



.scanty means that had preYionsly supported it. Similar instanoes are 

 fanuliaito careful observers, not the least interesting of which is that 

 of a broken Celery leaf which had sent out roots from the lowermost of 

 its wounded edges. 



Fig, V. — Leaf of Celery producing roots from thie lower edge of a woimd. 



The immediate cause of the formation of roots is involved in 

 obscurity, and is one of the most important parts of vegetable 

 physiology still to be investigated with reference to horticulture. 

 We all know how difficult it is to cause the cuttings of some 

 kinds of plants to produce young roots, and how rapidly they 

 are emitted by others ; it is to be supposed, that the difficulty 

 would be diminished in aU such cases, if we knew exactly under 

 what circumstances roots are formed. Nothing, however, 

 sufficiently certain and general to merit quotation has yet been 

 ascertained concerning this important property, which appears 

 to be connected with specific vitality, except the following 

 facts, viz. that roots are most readily, if not exclusively, formed 



