lUO 



mUKrnui^uisX ur i loour,.:). 



of the stem ; in Calodracon, according to Nageli, while the bundles and the fundamental 

 tissue become differentiated at the apex of the stem, a ring of meristem remains over, which 

 subsequently produces new bundles and secondary fundamental tissue. In Dicotyledons 

 and Conifers similar phenomena arise still more frequently and with many compli- 

 cations, the consideration of which I shall take up in Book II. Only one example may 

 here be described, since it will serve to show the relationship of the fundamental tissue to 

 the fibro-vascular bundles from a new point of view. In the hypocotyledonary segment of 

 the stem of Ricinus communis there is found on transverse section, at the commencement 

 of germination, a ring of generating tissue (Fig. 92, ^, x), by which the fundamental tissue 



VlG.g-z.—Ricznus commttnts ; transverse section through 

 the centre of the hypocotyledonary segment at various stages 

 of germination ; A after the appearance of the root beyond 

 the testa of the seed ; B after the hypocotyledonary segment 

 has attained a length of about 2 cm. ; C at the ead of germi- 

 nation ; 7)1 pith, r cortex, a- generating ring of tissue (corre- 

 sponding to Sanio's thickening ring) ; st medullary rays ; 

 fv fibro-vascular bundles ; ch connecting bands of secondary 

 meristem, producing xylem and phloem later, and forming 

 true cambium. 



Fig. 93.—^ a part of Fig. 92, more highly magnified ; sg- spiral vessels ; 

 ^j- bundle-sheath ; B the same ; true cambium is being formed by tan- 

 gential divisions in the fibro-vascular bundle now isolated ; the other 

 letters as in Fig. 92. Compare Fig. 82 (p. 95), which represents a part of 

 Fig. 92 C, magnified to the same degree as Fig. 93. 



is divided into pith (w) and bark (r) ; at this time eight groups of narrow spiral vessels 

 already indicate the differentiation of as many fibro-vascular bundles ; subsequently the 

 generating tissue (5) becomes differentiated' into eight completely isolated fibro-vascular 

 bundles (/t) and as many intermediate portions of parenchymatous fundamental tissue, 

 which is in no way distinguished from that of the pith and the cortex (cf. Fig. 93, JS); 

 the fibro-vascular bundles are now also separated by medullary rays. This condition, 

 however, does not last long, for as soon as the segment of the stem has become longer 

 and thicker, and the granular materials of the fundamental tissue are mostly consumed, 

 repeated divisions by tangential walls commence in those portions of the medullary 



