SECT. I MORPHOLOGY 21 



to 



The bud forming the growing end of a shoot is called the terminal 

 bud, while those borne on the sides of the shoot are the lateral buds. 



Shoots developing in predetermined positions on young parts 

 of the plant are designated normal, in contrast to adventitious 

 SHOOTS, which are produced irregularly from the old or young portions 

 of a plant. Such adventitious shoots frequently spring from old 

 stems, also from the roots of herbaceous plants (Brassica oleracea, 

 Anemone sylvestris, Convolvulus arvensis, Eumex Acetosella), or of bushes 

 {Euhus, Rosa, Corylus), or of trees (Populus, Ulmus, Bobinia). They 

 may even develop from leaves, as in Cardamine pratensis, Nastwrimm 

 officinale, and a number of Ferns. An injury to a plant will frequently 

 induce the formation of adventitious shoots, and they frequently arise 

 from the cut surface of stumps of trees. Gardeners often make use 

 of pieces of stems, rhizomes, or even leaves as cuttings from which 

 to produce new plants. 



Leaves and also normal shoots, which make their appearance as out- 

 growths from the portions of the parent shoot, still in an embryonic 

 condition, have an external or exogenous origin. Adventitious 

 shoots, on the other hand, Avhich arise from the older parts of stems 

 or roots, are almost always endogenous. They must penetrate the 

 outer portions of their parent shoot before becoming visible. Adven- 

 titious shoots formed on leaves, however, arise, like normal shoots, 

 exogenously. 



Buds are formed in the marginal indentations of tlie fleshy leaves of species 

 of Bryoiihyllum (Crassulaceae). Although arising from the leaf these buds 

 must properly be regarded as "normal," and as forming part of the normal 

 ontogeny of the plant, since they arise in }>re-determined positions from young 

 tissue. In the strict sense of the term only those buds can be called adventitious 

 which are produced in casual positions from tissues which in their production 

 enter into renewed activity, e.g. the buds which arise at the base of isolated leaves 

 of Begonia when these are laid on damp soil. The concept of "normal buds" is 

 notwithstanding usually taken in a narrower sense and limited to buds which 

 arise on the axis of the shoot in the normal course of development. Examples, 

 however, occur which make it difficult to draw a sharp distinction in this latter 

 sense between normal and adventitious shoot formation (^^). 



While, as a rule, new leaves arise beneath the apex of a stem, which continues 

 to grow, exceptions to this occur, especially in floral structures ; the apical cone 

 may be used up in the formation of a terminal leaf-rudiment. In this way some 

 of the stamens and carpels of Phanerogams, which are described as terminal, 

 arise. 



It was mentioned above that normal shoots arose from the embryonic tissue 

 of the growing point of the parent shoot. When they are apparent at a greater 

 distance froni the apex (Fig. 17) it can usually be shown that embryonic substance 

 has been reserved at the proper points for their formation. The growing points of 

 adventitious shoots are for the most part derived from embryonic tissues which 

 have persisted in the older portions of the plant and are cajiable of increase. 

 They can, however, also arise from older tissues, owing to the capability of the 

 latter to return to the embryonic condition and produce new growing points. 



