COURSE OF THE BUNDLES IN THE STEM. 253 



3. Bundles of the trace and cauline bundles are both present. The bundles of the 

 trace are arranged in a ring, the caulitie bimdles are in the pith. To this series belong 

 species of Begonia, Orobanchese, species of Mamillaria, Melastomaceae, some Um- 

 belliferse, and Araliacege : further in the main also Nelumbium. 



In the Begonias medullary bundles are common, Hildebrand^ found them in 28 

 species out of 128: for instance in B. Evansiana, laciniata, Rex, xanthina, etc. Accord- 

 ing to Hildebrand's description of stems in the mature state (following the course from 

 below upwards) these seem to be for the most part cauline. In the first internodes of 

 the seedling they are wanting, they branch from those of the ring in higher internodes. 

 They run parallel and perpendicular in the internode, in the nodes they anastomose with 

 one another and with those of the ring : as a rule none pass through the node without 

 connection with others. In B. Hiigelii, Muricata, and luxurians Hildebrand saw 1-3 

 medullary bundles enter, without previous anastomosis with others, directly into the 

 middle of the petiole, a phenomenon which occurs less frequently in others : e. g. 

 B. laciniata. From the plexus in the node medullary bundles pass on into the next 

 higher internode, and other bundles branch off to pass into the ring. In some stems 

 single bundles in successive nodes pass successively into the pith, and again into the ring, 

 and finally into a leaf, ' but this whole course is rendered very indistinct by anastomoses.' 



The many points, which still remain doubtful, arise partly from the difficulty of following 

 the course of the bundles in the Begonias with accuracy. It is made the more probable 

 that the medullary bundles are for the most part cauline by the fact that, according to 

 Sanio's investigation of B. Evansiana (A c. 224), they appear later than those of the ring^ 



Aralia racemosa^ and A. japonica have within the typical Dicotyledonous ring a 

 second, consisting of small, widely separated bundles. In other species, e.g. A. papyrifera, 

 the second ring is absent. Besides this ring there are, according to Sanio in A. racemosa, 

 other single bundles scattered in the pith. All these bundles, which run perpendicularly 

 in the internode, anastomose in the nodes without passing out to the leaves : their de- 

 velopment proceeds much later than that of the ring. As regards the distribution of 

 vessels and sieve-tubes the outer medullary bundles have a position the reverse of that of 

 the bundles of the ring, the inner ones are irregularly arranged. Comp. § loi. 



In the stem of some few Umbelliferx*, Silaus pratensis Bess., Peucedanum Oreose- 

 linum Mch., Opoponax Chironium K., Ferula communis, and an undetermined form of 

 Taurus, medullary bundles have been observed within the ring: as many as 13 in Silaus, 

 20 in Opoponax, 82 in the plant of Taurus (Reichardt), at least 100 in the flowering 

 stems of Ferula communis. .They are distributed in the transverse section over the 

 whole pith: their number varies in successive internodes, e.g. in Silaus, Ex. I. 13, ri, 10, 

 9, 7, 3 ; Ex. II. 10, 8, 7, 7, 6, I ; Ex. III. 9, 8, 5, 3, i : Peucedanum Oreoselinum, Ex. I. 

 22, 20, 18, 17, 14, 7; Ex. II. 20, 18, 17, 17, 12, 6; Ex. III. 15, 13, ro, 7, 3. 



According to the consistent accounts of Jochmann and Reichardt the medullary 

 bundles do not pass out into the petiole ; they are cauline. They take a parallel and 

 perpendicular course through the internode, dividing here and there, and united for 

 short distances : at the node they anastomose by means of connecting bundles with one 

 another, and with those of the ring : from the anastomosing bundles in the node those 

 medullary bundles start which traverse the next internode. Those of the lowest inter- 

 node above the root affix themselves on those of the ring of the same internode, or 



* Anatomische Untersuchungen liber die Stamme d. Begoniaceen, Berlin, 1859. 



* [Cf. Westermaier, Ueber das markstandige Biindelsystem der Begoniaceen. Regensburg, 1S79.] 

 ^ Sanio, I.e. p. 226. 



* De Candolle, Organographie, I. p. 184, Taf. III. — Jochmann, de Umbelliferarum structura, 

 18-^. — H. W. Reichardt, Ueber das centrale Gefassbiindelsystem einiger Umbelliferen, Wiener Acad. 

 Sitzungsbr. Bd. XXI (1856), s. 133. 



