COURSE OF THE BUNDLES IN THE STEM. 



269 



only frequently united within the stem, but are connected in a reticulate manner by 

 anastomoses. Many forms, such as Syngonium, are transitional between the second 

 group and the third. In small branches of rhizomes of Richardia aethiopica also the 

 typical curved course may be easily recognised, especially in the ends of the branches ; in 

 Alocasia, Dracunculus, Caladium esculentum the system of vascular bundles forms 'a 

 complicated net, in which it is impossible, by the most careful dissection of a macerated 

 stem, to trace one bundle with certainty even for a short distance.' Still even here it 

 may constantly be recognised, especially at the apex of the stem, how the bundles pass 

 from the base of the leaf with a curved course to the middle of the stem, and from thence 

 downwards and outwards. 



Fig. 119. 



Fig. 120. 



Figs. 119 and 120. — Tradescantia albiflora. Fig. 119. Outline and vascular bundle-system of the end of a stem cleared by 

 potash, and divested of part of the cortex and cylinder by longitudinal sections. The surface of section is turned towards the 

 observer. Those bundes which in this position run in a higher plane are drawn darkly, those in lower planes more lightly. 1 he 

 successive leaves are indicated by the figures i — 5 ; leaf 6 is just formed at the growing-point ; opposite the median bundle of i 

 is an axillary bud. The bundles of leaves i, 2, and 3 are visible ; y the separate, / the united portions. From 3 are to be seen 

 four markedy"; two of these (right of the median line) run into the leaf; two others, median and anterior, are cut off at their 

 point of exit. From leaf 2 are three marked _/"; the middle one cut off. The lines s show the course of the cauline bundles. 

 Magnified about 25. 



Fig. 120 (40). — Transverse section through a young internode. In the middle the four united bundles; externally eight 

 separate ones, the three principal ones marked d; then the circle often cauline bundles. 



IV. Type of the Commelinace^e. 



Sect. 69. The bundles in the stem of those Commelinaceae which have been 

 investigated, and of many Potamogetons, have a course which differs from that of 

 most Monocotyledons, and resembles rather that of the Piperaceae (p. 249) and 

 Mirabilis (Chap. XVI). This is seen particularly clearly in the plant widely known 



