300 JOUKXAL OF THE ROYAL HORTICULTUEAL SOCIETY. 



the nutriment at once goes to the bulbs, consisting of two or three fleshy 

 leaves, with a minute bud between them. 



I have mentioned that whatever property a plant may possess, or have 

 acquired, it is not only in the possession of the special part of the plant 

 where it is usually localised, but it is held in a potential way in every 

 portion of protoplasm. Thus, though, judging from analogy, the tubers 

 of a potato-plant were originally formed by the obstruction of the soil to 

 the elongation of its underground branches ; yet, if they be prevented 

 from forming altogether underground, by their constant removal as soon 

 as they appear, then the aerial branches will be arrested and assume the 

 form of axillary tubers. Again, cuttings of potato-branches, instead of 

 striking root, will often form tubers instead ; and a potato left in a dark 

 cellar sent out numerous colourless branches from the "eyes," and these, 

 too, bore numerous small tubers all over them. 



ProjJCigative Lcares. — Leaves can both normally and abnormally pro- 

 duce roots and buds, and so give rise to independent beings. Familiar 

 examples are Bryopliylliim calycinum and Asplenmm Imlhifcrum ; but 

 several other Ferns are also liable to the production of propagative buds. 

 The Water-cress and Lady's Smock do so occasionally, and several plants,, 

 as Gloxinias and Begonias, are habitually propagated artificially by means 

 of the leaves alone. In the former, the buds are borne by the leaves in 

 air ; but in the latter case the leaves require the stimulus of a damp soil 

 to produce them. 



" The first change observed " (write Drs. Kerner and Oliver*) " in 

 a leaf which has been cut off for the purpose of forming cuttings is the 

 desiccation of the cells Ipng next to the cut surface. Beneath the layer 

 of dried-up cells a cork-tissue is formed, whilst the dead, outer layer is 

 converted into bark. A parenchymatous tissue is next formed from the 

 part beneath the cut which is still living ; indeed, it is the epidermal cells 

 nearest to the dead layer of cells that initiate this formation of tissue. 

 They gro"\v in a radial direction, elongating and dividing by means of 

 the insertion of transverse walls, the result being a uniform thickening 

 coextensive with the surface of the wound. A little later some of the 

 living cells in the middle of the cut, which are still covered over by the 

 dead layer, begin to divide ; and as the tissue there grows in size, it tears 

 the overlying dried layer into shreds and pushes it of!" in parts. This 

 exuberant tissue has received the name of ' callus.' 



" In order to secure water from the soil, the leaf now develops absorb- 

 ing cells resembling ordinary root-hairs. AYhen the callus has acquired 

 a sufficient growth, numerous roots are formed. They issue from the layer 

 of cells adjacent to the vascular bundle of the leaf, probably homologous 

 with the pericycle of the root ; they break through the callus and pene- 

 trate the soil. Then buds begin to appear on the upper side of the leaf, 

 issuing from the callus." 



In all cases, whether normal or not, the appearance of leaf-buds shows 

 that it is a property of plant-life which resides in the protoplasm of every 

 linng part of the plant. 



Buds Beplacing Floivers. — A compensatory process between the vege- 



* Tlic Natural History of Plants, ii. p. 42. 



