VEGETATIVE MULTIPLICATION. * 615 



Morphology of Stems (p. 20 et seq.} and Buds (p. 69). We have there 

 spoken also of the formation of adventitious buds (p. 70) and cited nume- 

 rous examples strongly indicating that relative independence of the parts 

 of the organization of plants referred to above. 



Adventitious Buds are formed mostly when a plant or part of a plant 

 loaded with assimilated nourishment is deprived of its natural developing- 

 points. Thus we see ahundant formation of adventitious buds on healthy 

 trunks of trees wliich have been pollarded, i. e. have had their heads cut 

 down so as to remove almost all their natural buds. Sometimes the shoots 

 so produced simply result from the development of otherwise dormant 

 buds. The abundant supply of food existing in the trunk, however, often 

 stimulates the cells of the cambium-reyion (p. 530) into extraordinary de- 

 velopment, and true endogenous leaf-buds are produced, which form vents 

 for the vital energy of the plant. This power exists even in the roots of 

 many trees, as in Madura aurantiaca, Pyrus japonica, &c., fragments of 

 which in a healthy condition may be made to produce new plants. The 

 buds so formed are of endogenous origin, arising in or near the cambium- 

 region. 



Mention has been made of the formation of adventitious buds (as exo- 

 genous formations) on leaves, which has been observed frequently in wild 

 plants, and is artificially induced in many cases as a means of propagation. 

 As a rule, leaves are less prone to produce buds than stems or even roots, 

 as might be expected from the more actively changing state of the con- 

 tents of their tissues, and the usual absence of any great accumulation 

 of assimilated substance, such as is regularly met with at certain periods 

 in the stem and root. 



That striking characteristic of vegetables which displays itself in the 

 physiological independence of the leaf-buds, renders the vegetative propa- 

 gation of plants a most important feature in their history, both in a natu- 

 ral and, in a still higher degree, in a cultivated condition. 



A brief notice of some striking phenomena illustrative of the spon- 

 taneous propagation of the higher plants may be given here. 



Various herbaceous plants are multiplied by spontaneously detached 

 axillary leaf -buds : of this we have f amiliar examples in Lilium bulbiferum, 

 Dentaria bulbifera, and the cultivated species of Aclrimenes. Similar pro- 

 pagative buds are often produced instead of flowers in the inflorescence 

 of the species of Allium (Garlic, &c.), both in a wild and cultivated con- 

 dition : and the same is the case with some other plants, such as Polygo- 

 num viviparum, &c. 



The multiplication of bulbs by " cloves," or axillary bulbs produced in 

 the axils of the scales of the parent bulbs, has been described in a former 

 Chapter (p. 25), and there also have been mentioned the structures called 

 tubers, formed of modified stems, which are important agents in propa- 

 gating the plants in which they occur. The Potato, for instance, forms 

 tubers from its branches, the " eyes " or buds of which may be separated 

 and made to produce each a new plant : and the Jerusalem Artichoke, 

 Dahlia, &c. are similar in this respect. The terrestrial Orchids, such as 

 Orchis Morio (tig. 21) &c., are not multiplied by their tubers, but only 

 continued from year to year, since only one new " eye " is formed annually. 

 Still more frequent, perhaps, than the formation of bulbils, bulbs, or 

 tubers is the development of leafy shoots peculiarly organized for the 



