27i INSTANCES OF LEAVES ROOTING. 



plant, when the'centralpart of the stem was decayed. Finailly,:. 

 the following case is named in the same work (vol. v. p. 242) by 

 Mr. Knight :— " In an early part of the summer, some leaves 

 of Mint (Mentha piperita), without any portion of the substance 

 of the stems upon which they had grown, were planted in small) 

 pots, and subjected to artificial heat, under glass. They 

 emitted roots, and lived more than twelve months, having 

 assumed nearly the character of the leaves of evergreen 

 trees ; and upon the mould being turned out of the pots, it was 

 found to be everywhere surrounded by just such an interwoven 

 mass of roots, as would,have been emitted by perfect plants of 

 the same species. These roots presented the usual character 

 of those organs, and consisted of medulla, alburnum, bark, and 

 epidermis ; and as the leaf itself, during the growth of these, 

 increased greatly in weight, the evidence that it generated th"e 

 true sap which was expended in their formation appears 

 perfectly conclusive." 



In gardens, we have many other cases of the same kind. 

 Hoya is a common instance, and three others are here figured 

 (Fig. XXXVIII.); viz., Gesnera (a), Clianthus puniceus (b), 

 Gloxinia speciosa (c). In these, and all such cases, the first 

 thing that happens is an excessive development of cellular 

 tissue, which forms a large convex " callus" at the base ; from 

 which, after a time, roots proceed ; and by which eventually a 

 leaf -bud, the commencement of a new stem, is generated. 



It is not surprising that leaves should possess this quality 

 when we remember that every leaf does the same thing 

 naturally, while attached to the plant that bears it ; that is to 

 say, forms at its base a bud which is constantly axillary to 

 itself. Leaves, however, have not been often employed as the 

 means of propagating a species ; and it is probable that most 

 leaves, when separated from their parent, are incapable of 

 doing so, for reasons which we are not as yet able to explain. 

 The most common case of their employment is in the form of 

 \ the scales of a_bulbj_which will, with some_cejiainty, produce 

 new ^aEtr-imder favourable circumstances. ThQSfi—circum- 

 stances are, a strong bottom heat, moderate moisture, and a 

 rich stimulating soil. 



