July 13, 1888.] 



SCIENTIFIC NEWS. 



33 



BUDS. 



(Continued from page 10.) 

 TN order to understand clearly the formation of a bud, 

 whether lateral or terminal, it will be necessary to 

 briefly trace its development from this conical mass of 

 embryonic tissue. The earliest differentiation has been 

 detected in the growing point itself, where in the almost 

 homogeneous tissue the three layers of cells which form 

 the various structural systems of stems and leaves are 

 very faintly marked out. These three layers are the 

 Plcrome, which produces the pith and fibro-vascular 

 system; the Pcriblem from which the cortex or bark 

 arises ; and the Dermatogen, from which the epidermis or 

 skin is formed. The mode of growth by which these 

 three layers arise is that of cell-division and in flowering 

 plants it is confined to the growing point and to another 

 region of similar tissue known as the cambium. The 

 further we proceed downwards from the growing point, 

 which seldom amounts to more than the hundredth part 



Fig. 



f ? l f 



3 (after Prantl).— Diagram of a longitudinal section of 

 the stem of a dicotyledonous plant, m, pith ; f, fibro- 

 vascular bundles, both developed from the plerome pi, 

 the bundles sending branches to the leaves ; r, cortical 

 tissue ; e, epidermis ; 66, young leaves, two showing their 

 origin from the protomeristem, p ; kn, axillary bud. 



/ 



Fig. 5 (after Bentley ). — a, vertical section of a reclinate leaf ; 

 6, transverse section of a conduplicate leaf; c, transverse 

 section of a plaited or plicate leaf; d, vertical section of 

 a circinate leaf; e, transverse section of a convolute 

 leaf ; _/, transverse section of a revolute leaf; g, trans- 

 verse section of an involute leaf. 



of a millimetre, the more clearly defined do these three 

 layers and the systems subsequently developed from them 

 become, until they attain the readily recognisable cellular 

 and vascular distinctions of form previously described. 

 The leaves are always developed in a regular order, viz., 

 acropetally, or from base to apex, as may be easily 



observed on expansion — and they always take their rise 

 from the outer layer or layers of the sides of the growing 

 point before the epidermis is formed, and in their earliest 

 visible condition appear as little roundish or conical 

 swellings, as shown, in figs. 1 a and b, 3 b and kn. As 

 before stated, they never arise from the actual apex 

 of the growing point, because their so doing would stop 

 further growth in that direction, as is the case when a 

 stem ends in a flower (lilac and horse-chestnut, fig. 4.) 

 As they form they carry out with them in continuity the 



Fig. 4 (after Sachs,). — Median longitudinal section through a 

 vigorous winter bud of the Horse Chestnut (Acscitlus 

 hippocastanuni). m, pith ; h, wood and r cortex of the 

 shoot axis (vr) of the preceding year ; ss, bud 

 scales; //, young foliage leaves — in the middle are the 

 flower buds. Woolly hairs fill the dotted space. 



vascular, cortical, and epidermal tissues of the stem. 

 Thus in our bud we have pith, fibres, and vessels sur- 

 mounted by an apex of dividing cells from which rudi- 

 mentary leaves proceed, whilst lower down the leaves 



Fig. 6 (afle- Bcn'ley)— Transverse section of buds: a, to show 

 the leaves arranged in a valvate manner ; 6, to show 

 imbricate vernation ; c, to show twisted or spiral verna- 

 tion ; d, to show induplicate vernation ; c, to show edui. 

 tant vernation ; f, to show obvolute vernation, and g 

 to show supervolute vernation. 



are in a more advanced condition with vascular, 

 cortical (modified) and embryonic systems of their 

 own and embryonic buds in, their axils. This is 

 the condition of the structure in autumn, and such 

 it remains during the dormant period of winter until 



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