254 



PRIMARF ARRANGEMENT OF TISSUES. 



rather spring from tliein : tlie same is the case witli those of the lowest internode of a 

 branch, so that the latter are not in direct continuity with those of the stem (Reichardt). 

 The occurrence of medullary bundles is a purely specific property. Of eight investigated 

 species of Pcucedanum they appear only in P. Oreoselinum : they are absent in Silaus 

 tenuifolius. They are not present in the one-year-old seedling of S. pratensis. 



Some Mo>7iillorias ^ have, within the typical ring of bundles of the leaf-trace, a second in 

 the peripheral parts of the pith, this being composed of numerous small cauline bundles, 

 la INI. angularis, and an undetermined similar species, there are about thirty of these. 

 They ascend the stem parallel to those of the leaf-trace, are strongly undulated in a 

 radial, and especially in a tangential direction, and anastomose at acute angles. They are 

 absent in young seedlings and in young shoots, and appear later at some height above 

 the base of the shoot, springing from the inner side of the bundles of the trace. I was 

 unable to find anastomoses with the leaf-trace, or the ring of secondary wood, excepting 

 at their point of origin. In other Mamillarias, as M. pusilla, glochidiata, &c., I looked 

 in vain for the medullary bundles, even in the mature shoot. Of other Cactaceae, forms 

 of Echinocactus and thick ones of Cereus (e.g. C. candicans?) have a medullary system 

 of bundles, which on account of its peculiar relation to the lateral shoots will be described 

 in Sect, 94. 



The small Orobancbex have in their stems only the typical Dicotyledonous ring of vascular 

 bundles. Strong stems of the more robust forms, as O. elatior Sutt., rubens Wallr., 

 caryophyllacea Sm., Rapum Thuill., and Cistanche lutea^, have, 

 inside the ring, and scattered in the pith, small bundles, the 

 number of which is variable, and is large in strong specimens. 

 They are cauline, and in young specimens take an undulating 

 longitudinal course through the stem, anastomosing here and 

 there, and ending blind beneath the apex of the stem. Comp. 

 Fig. 111. In fully developed flowering stems they gradually cease 

 below the inflorescence, curving outwards, and uniting with the 

 bundles of the ring. It is only in Cistanche lutea, where they 

 occur in considerable quantity, that they run freely in large num- 

 bers to the extreme apex of the inflorescence. In Eplphegus 

 americanus and Conopholis ^ there are found in the base of the 

 main stem three concentric rings of bundles : in the latter genus 

 the bundles composing them are contiguous with one another in 

 radial series. It is uncertain whether these belong to this category, 

 or to that of radially diverging bundles of the trace, or are pro- 

 ducts of a secondary cambium. 



In the flowering stems of species of Balanophora, according 

 to Goppert's* description, the same or a closely similar arrange- 

 ment occurs to that in O. Rapum : numerous branched bundles are scattered within a 

 ring composed of bundles of the leaf-traces. 



In the Helosideae the ring of bundles is alone present in the elongated rhizomes, in 

 the tubers and Inflorescences there are branched, scattered bundles'*. 



Two cataphyllary leaves and one foliage leaf succeed one another regularly on the 



Fig. III.— Orobanche Rapum 

 (natural size). Bud of a flower- 

 ing shoot, median longitudinal 

 section, b — b ring of bundles, 

 consisting of leaf-traces ; witiiin 

 this are the cauline bundles. At 

 the base, where it has been cut 

 off, is a network of the latter, 

 which anastomose one with an- 

 other, and with the bundles of 

 the leaf-trace. 



' Von Mohl, Verm. Schriften, p. 115. 



^ Graf zu Solms-Laubach, de Lathrsese generis positione systematica, Diss. Berlin, 1865, pp. 8, 

 14, and Pringsheim's Jahrb. VI. p. 522. 



3 Chatin, Anat. Comp. Taf. XVIII. 



* Ueber den Ban der Balanophoren, N. Act. Carol. Leop. vol. XVIII. Suppl. i. — Compare also 

 Hooker, Balanophorex-, Trans. Linn. Soc. London, XXII ; Graf zu Solms, in Pringsheim's Jahrb. 

 /.r. p. 529. 



^ Compare Eichler, in Flora Brasiliensis, Fasc, XLVII. 



