THE FUNDAMENTAL TISSUE. 



07 



schaftliche Botanik, IV. p. 23; Kraiis, ditto, IV. p. 305, and V. p. 83; Borscow, ditto 

 VII. p. 344.) 



(d) Nenv formations in the fundamental tissue. The collective fundamental tissue in 

 the stem of the higher Cryptogams, in the stem of most Monocotyledons and of many 

 Dicotyledons, as well as in all leaves, and in all roots not yet changed by growth in 

 thickness, originates immediately from the primary meristem of these organs by further 

 development, simultaneously with the fibro-vascular bundles and the epidermal tissues. 

 In the stems and roots of many Phanerogams endowed with growth in thickness, it occurs, 

 however, that within the fundamental tissue, 

 either originally or subsequently, meristem 

 is formed, out of which secondary funda- 

 mental tissue, together with secondary fibro- 

 vascular bundles, is then produced. This 

 behaviour is seen very clearly in the stem 

 of Dracaena, Aletris, Yucca, Aloe, Lomato- 

 phyllum, and Calodracon \ In Dracaena and 

 Aletris isolated fibro-vascular bundles are 

 formed in the primary meristem of the apex 

 of the stem, while the whole fundamental 

 tissue which surrounds them and separates 

 them from the epidermis is transformed 

 into parenchyma, and passes over into per- 

 manent tissue ; but after considerable time 

 (in Aletris flagrans about 4-5 cm. below 

 the apex of the stem, in Dracana reflexa, 

 according to Millardet, as much as 17-18 

 cm. below the apex) a fresh formation 

 of meristem begins in one of the cell- 

 layers of the fundamental tissue which 

 immediately surround the outermost fibro- 

 vascular bundles ; the permanent cells con- 

 cerned in it divide repeatedly by tangential 

 walls ; and there arises (seen in transverse 

 section) a girdle of meristem (Fig. 91, .v), 

 the cells of which are arranged in radial 

 rows. In this meristem new fibro-vascular 

 bundles are produced ; one, two, or more 

 adjoining cells of the transverse section 

 dividing repeatedly by longitudinal walls 

 in various positions. Out of the procam- 

 bium-bundles which arise in this manner 

 the cells of the fibro-vascular bundles pro- 

 ceed immediately ; the intermediate meristem passes over likewise into permanent tissue, 

 and indeed into strong-walled parenchyma, which now forms the secondary fundamental 

 tissue between the secondary fibro-vascular bundles. Since the cells of the thickening- 

 ring which face inwards pass over in centrifugal succession into permanent tissue, 

 while the outermost divide repeatedly, the whole ring continually moves centrifugally, 

 and leaves behind the new bundles and parenchyma-cells. In Yucca Millardet found 

 the origin of the ring of meristem (thickening-ring) as little as 3mm. below the apex 



FiC. 91.— Part of the transverse section of a stem of Dra- 

 crena (probably reflexa) about 13 mm. thick and i metre higli, 

 about 20 cm. below the summit, e epidermis; k cork (peri- 

 derm) ; r cortical portion of the fundamental tissue ; b trans- 

 verse section of a fibro-vascular bundle, bending out to a leaf; 

 ni the primary fundamental tissue (pith) ; g the primary bundles ; 

 X the girdle of meristem in which very young fibro-vascular 

 bundles are to be seen, while the older ones g have already 

 partially or entirely passed out of it, its lower part becoming 

 transformed into radiately arranged fundamental tissue [st). 



' Compare Millardet's description, Sur I'anatomie et le developpement du corps ligneux dans 

 les genres Yucca et Dracaena (Extrait des Mem. de la societe imper. des sciences nat. do Cherbourg, 

 F. XI, 1865 ; and Nageli, Beitrrige zur wissen. Botanik. Heft i, p. 21). 



