ORGANS OF >arrRITION. 97 



various other points than the axils of leaves ; these are called, 

 from their abnormal origin, adventitious : and, Thirdly, by the 

 formation of accessory buds. 



1. Non-devehp'/neiif of the regidar bnds. This frequently takes 

 place irregularly, and is then 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 instances, 

 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 spire, 

 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 that they appear to grow in a 

 circle. 



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 

 oflF, the latter becomes gorged with sap, and a multitude of ad- 

 ventitious 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 their non-development. 



In every instance the adventitious buds take their origin from 

 parenchymatous tissue : thus, if produced on the stem or branches, 

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

 they may arise from the margin, as in Malaxis paludosa {fig. 

 1 88, h, b), Q.ndiBryophyllumcalyoinum{ fig. 1 87). or from the surface, 

 as in Ornithogalum thyrsoideum {fig. 1 89, 6, b, b). Leaves thus bear- 

 ing buds are QQWedi proliferous. Such buds are naturally formed 

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

 they may also be produced artificially on various leaves, such as 

 those of Gesnera, Gloxinia, and Achirnenes, by the infliction of 

 wounds, and afterwards placing them in a moist soil and ex- 

 posing them to the other influences which are favourable for their 

 growth. The buds developed on the leaves in such cases ulti- 

 mately form independent plants, and this methotl is constantly 

 resorted to by gardeners as a means of propagation. These ad- 

 ventitious buds differ from those commonly produced in the axil 

 of leaves, or at least from those which remain dormant during 

 the winter ; thus they are smaller, and have no external protec- 

 tive organs or scales. 



