59° 



SECONDARY CHANGES. 



Sect. 192. The families of the ChenopodiacecB, AmarantacecE, Nydaginea, Mes'em- 

 bryanlhema, and according to Regnault also the Tetragoniea, and as far as is 

 known all their congeners, show a series of anomalies of growth and structure, 

 corresponding in certain main features, but with various differences in detail within 

 the same family and even the same genus. With these may be connected Phytolacca 

 among the Phytolaccacese, while in the genus Rivina (R. brasiliensis and aurantiaca), 

 placed in this family, the stem and root have normal growth and thickening ^. 



The common peculiarity of structure of the parts in question consists in the 

 fact that the secondary thickening, within the annular active cambium zone, contains 

 more than one circle of distinct collateral vascular bundles showing a limited growth: 

 these are embedded in unlike tissue, which may be generally termed interfascicular 

 or intermediate tissue. 



This structure, in its individual forms, originates in different ways. 



1 . A primary ring of bundles appears in the stem, and in the roots the primary 

 axile bundle : in both there is first a normal cambium with normal products. The 

 activity of the latter then ceases, and around it appear in centrifugal order suc- 

 cessively renewed and disappearing cambiums, each of which forms a circle of dis-' 

 tinct vascular bundles. This mode occurs in all investigated roots of plants of this 

 category with the exception of those to be named under (3) ; further, in the stem of 

 Phytolacca, and, judging from Regnault's statements, which require corroboration, 

 also of Tetragonia and Sesuvium ; according to the individual case the successive 

 rings are variously complete and regular. 



2. In a number of stems there is at first a primary ring of bundles, consisting 

 of leaf-trace bundles, and often perhaps of intercalary bundles also (p. 456);- in 

 species of Amarantus (p. 249) there are also medullary leaf-traces. ~ While the 

 development of the collateral bundles is still proceeding there appears round the outer 

 margins of their phloems a ring of cambium, which is accordingly extrafascicular ; 

 this remains permanently active, and forms on its inner side alternately collateral" 

 vascular bundles and intermediate tissue, on its outer side a thin layer of bast, 

 consisting only of parenchyma, or even no bast at all. This is the case in the 

 investigated stems of shrubby Mesembryanthema, the stalks or stems of Mirabilis, 

 Oxybaphus, and of all Nyctagineae (Pisonia, Boerhavia, Bougainvillea, "Neea) ; of 



' Literature: — ChenofodiacecE. Unger, Dicotyledonenstamm, I.e., p. 260. — Von Gemet, Ueber 

 den Bau des Holzkbrpers einiger Chenopodiac, Bull. Soc. Imp. de Moscoii, 1859, I. p. 164. There 

 is there quoted : Basiner, in von Baer and Helmersen, Beitr. z. Kenntn. d. Russ. Reichs, Bd. XV. — 

 Sanio, Botan. Zeitg. 1863, p. 410; 1864, p. 225. — Regnanlt, in Ann. Sc, Nat. 4 s^r. torn. XIV. 

 (i860). 



Amarantacea. Link, Elem. Phil. Botan. ed. i, p. 444. — Unger, Regnault, I.e. — Sanio, Botan. 

 Zeitg. 1864, p. 229. 



Nyctaginem. E. Meyer, de Houttuynia, p. 40.— Unger, Regnault, /. r.— Nageli, Beitr. I. p. 119. 

 — Sanio, I.e. 1865, p. 197. — Finger, Anatomie u. Entw. von Mirabilis Jalapa, Diss. Bonn. 1873. — 

 Gronlund, Stammens og Grenens anatom. Bygning hos Neea Iheifera sammenholdt med andre 

 Nyctagineer. Vidensk. Meddelels. nat. Forening Kjobenhavn, 1872, p. 6o. 



Mesembryanthemum. Regnault, /. c— Falkenberg, in Gottinger gel. Anzeigen, 1876, p. 99. 

 Botan. Zeitg. 1876, p. 317. [Also Petersen, Bot. Ztg. 1878, p. 785.] 



Fhytolacea. Martins, Revue horlicole, 1855, p. 123 (Botan. Zeitg, 1856, p. 582).— Treviranus, 

 Botan. Zeitg. 1856, p. 833.— Regnault, /.r.— Nageli, Beitr. I.e. pp. 26, 118." 



