CLAYTONIA GRONOV.— THEO. HOLM. 33 



But in these we notice a more or less distinct layering, like annual rings, which have been pro- 

 duced by the continuous formation of independent groups of leptome with a few vessels in the 

 secondary cortex. These rays of collateral mestome-bundles are furthermore separated from 

 each other by broad rays of pith. The central cylinder, with the primordial groups of leptome 

 and hadrome, is hardly discernible in these thick roots; the entire central group of these tissues 

 is mostly destroyed, and the root shows generally a broad, hollow center. 



While examining some older roots of this species we often noticed that the long, lateral 

 ramifications showed a tendency to grow together in several places, thence to become separated, 

 and sometimes to grow together again at a greater depth (pi. 1, tig. 4). The complete preser- 

 vation of the central cylinders in such roots, where they were free and where they had grown 

 together, seems to prove that a fusion had actually taken place rather than a cleaving of a single 

 root. Another peculiarity which was frequently observed in the very thickest portion of the 

 root was that the internal structure did not only show one central cylinder with its heavy mass 

 of secondary cortex, but also several much smaller and apparently independent mestome-cylinders. 

 Considering the fact that each of these mestome-cylinders possessed exactly the same structure 

 as that of a slender root, viz, that it was covered by several layers of cork surrounding a 

 secondary cortex and a central portion of leptome, cambium, and vessels, make us believe that 

 these represent lateral roots, and that they remain inclosed within the loose and very heavy coat 

 of cork layers, which is always noticeable in matured roots of this species. In some cases, 

 especially where several of these mestome-cylinders were massed together, some of these showed 

 the same tendency to melt together as the free roots; but also in these were the central cylinders 

 perfectly isolated, and the only tissues in which the fusion was observable was the cortex and 

 the cork, the latter forming one single coat around two of these mestome-cylinders. The thick 

 root of ('. megarrhiza thus represents the primary root of the plant, and it persists for several 

 years, with a gradual increase in thickness. The thickness, however, does not seem to be due 

 only to the formation of secondary tissues within the main root alone, but also to the develop- 

 ment of lateral roots, which not only increase in thickness themselves but which, furthermore, 

 remain inclosed and covered by the cork of the primary root. 



Similar cases of roots being inclosed has been described as characteristic of some other 

 plants, for instance: Bromeliacese," Erioca/ulaceae, b and Ophrydese." 



In Claytonia Virginia* L., the underground, dark-brown, tuberous body from which the flower- 

 ing stems and leaves proceed is generally described as a tuber, or sometimes as a conn, but, as 

 stated above, this organ represents a root, the base of the primary. The long, filiform apex of 

 the main root (PI. 2, tig. 10) dies off during the first season, while the basal portion persists, and 

 increases gradually in thickness; it soon becomes globular, but when it is fully matured it repre- 

 sents a more or less laterally compressed body, with a roundish outline. At this stage numerous 

 filiform lateral roots are observable; they appear in small tufts on the edges of the mother root, 

 which is yet very distinctly diarchic. The minor structure of these roots at their various stages 

 is as follows: The lateral roots are of two kinds, some that are capillary, smooth, and almost 

 unbranched, and others that are thicker, prominently wrinkled and ramified. Of these the latter 

 develop from the central cylinder of the mother root, while the former appear as basal lateral 

 ramifications of these. The wrinkled roots are able to increase in thickness, but only a little, 

 and they never attain the swollen appearance of the mother root. Their increase in thickness 

 depends upon the divisions of the pericambium developing a cork outward and a secondary 

 cortex inward, throwing off the older tissues from the epidermis to the endodermis inch; a 

 cambial tissue has also developed to the same extent as described under ( '. megarrhiza. 



The most noticeable characteristic of these roots is their contractile power, which is effected 

 by means of a wrinkling of the cork layers, in which the radial cell walls show very distinct 

 undulations. A much more simple structure is possessed by the smooth and slender ramifica- 



" Jorgensen, A.: Bidrag til Rodens Naturhistorie ( Bot. Tidsskr. Copenhagen, ser. 3, vol. 2. 1877-79. p. 150. 



^The author: Eriocaulon decangulare L. (Bot. Gazette, vol. 31. 1901. p. 23). 



,; Same: The root structure of North American terrestrial Orchidese (Am. Journ. of Sc, vol. IS. 1904. p. 208). 



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