ORGANS OF NUTRITIOX. 103 



regular buds not being developed. Secondly, by the development 

 of other buds which are not placed in the axils of leaves, but 

 which arise irregularly at various points; these are called, from 

 their abnormal origin, adventitious: and, Thirdly, by the for- 

 mation of accessory buds. 



First, as to the non-development of the regidar buds. This 

 frequently takes place iiTegularly, and is altogether owing to 

 local or special causes; thus, want of light, too much crowding, 

 or bad soil, may cause many buds to become abortive, or to 

 perish after having acquired a slight development. In other in- 

 stances, however, this non- development of the buds takes place in 

 the most regular manner; thus, in Firs where the leaves are very 

 closely arranged in a spiral manner, the branches, instead of 

 presenting a similar arrangement, are placed in circles or rings 

 round the axis, at distant intervals. This arises from the non- 

 development of many of the buds of the leaves forming a spu-e, 

 which is followed by the development of the buds in the axils of 

 other leaves successively, and as such leaves are thickly placed, 

 we are unable, after the development of the branches, to trace 

 clearly the turns of the spire, so tliat they appear to grow in a 

 circle. Many other instances might be adduced of the influence 

 of the non- development of the regular buds, but the above will 

 be sufficient for our purpose. 



2. Adventitious Buds. — These have been found on various parts 

 of the plant, as on the root, to be afterwards referred to, the woody 

 part of the stem, the leaves, &c. Thus, when a tree is pollarded, 

 that is when the main branches on the apex of the stem are cut 

 off", the latter becomes gorged with sap, and a multitude of 

 adventitious buds are formed from which branches are produced. 

 The branches thus produced by pollarding, are, however, to a 

 certain extent caused by the development of other regular buds 

 which had become latent from some of the causes already alluded 

 to as interfering with then* non-development. In every instance 

 the adventitious buds take their origin from parenchymatous 

 tissue : thus, if produced on the stem or branches, it is from the 

 ends of the medullary rays ; when developed upon leaves, they 

 may arise from their borders as in Malaxis paludosa {fig. 196) 

 and Bryophyllum calycinum {fig. 195), or fi-om their surface as 

 in Ornithogalum tliyrsuideum (fig. 197). Leaves thus bearing buds 

 are called proliferous. Such buds ai'e naturally formed on the 

 leaves of the above plants, and occasionally on others, but they 

 may be also produced artificially on various leaves, such as 

 those of Gesnera, Gloxiiiia, and Achimenes, by the infliction of 

 wounds, and then placing them in a moist soil and exposing 

 them to the other influences which are favourable for their growth. 

 The buds developed on the leaves in such cases ultimately form 

 independent plants, and this method is constantly resorted to by 

 gardeners as a means of propagation. It would appear that 

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