ANOMALOUS THICKENING IN DICOTYLEDONS AND GVMNOSPERMS. 6oi 



Connecting bundles between the successive rings are found, according to Nageli, only in 

 the nodes. 



Sect. 193. In the anomalies thus far described the increase in thickness some- 

 times takes place like the normal increase in centrifugal progression ; neglecting 

 possible pathological states, the growth of the tissue within the cambium, which 

 is at the time active, is soon ended and disappears. Another condition was 

 only casually indicated for many of the cases hitherto described. We must now 

 return to these in connection with others. 



There are a number of parenchymatous stems and roots in which the old 

 parenchyma, far distant from the active cambium, has in all regions of the trans- 

 verse section, not only the power of growth and formation of new tissue, which it 

 puts forth when wounded and so on, but also in the uninjured plant it really grows 

 continuously, increases the volume and number of its cells, and produces secondary 

 meristem, from which strands of wood and bast, and cambium may be derived. 

 Leaving on one side the phenomena in the Cycadese, Sect. 195, which do not 

 strictly belong to this category, it has never been accurately investigated how far 

 the mature non-parenchymatous elements follow this growth. As far as appearance 

 goes, they seem usually to play a passive part. 



A number of the most peculiar anomalies owe their origin to these phenomena 

 of growth and secondary development. 



From the first series, viz. the stems of Lianes, Criiger quotes a number of 

 phenomena of this category, which require more exact investigation. Thus the 

 zones of intermediate parenchyma between the old successive thickening layers of 

 Securidaca volubilis are said to grow continuously broader, while room for this 

 growth is provided by widening of the radial bands of parenchyma in the rings 

 outside it. Cruger gives the same information for the Dilleniacese. 



Much more extended processes of growth and secondary formation, which 

 fundamentally alter the whole arrangement of the tissues and even the form of the 

 stems, occur in the Bauhinise, many Malpighiacese, Urvillea, and Bignoniaceae. 



The originally regularly formed and continuous xylem is here split into pieces 

 by growth, i. e. extension and cell division of the bands of pith and xylem- 

 parenchyma : these pieces have an independent growth in thickness by means 

 of a cambium surrounding them, which is in part undoubtedly a secondary forma- 

 tion, and which forms bast also on the side turned away from the wood. In 

 addition to the repeated splitting of the already formed strands of wood, new 

 ones with a further individual growth may be formed from secondary meristem. 



The splitting of the wood, described above, pp. 574, 375, for certain genera of Bigno- 

 niacese, occurs e. g. in the simple and diagrammatic case of Anisostichus capreolata 

 (Fig. 2 3 7 ), since, after being stationary for years, extension and division of parenchymatous 

 cells begins in the pith, and, extending from the pith radially towai-ds the four plates of 

 bast, splits up the wood into its four main segments. The segments of wood, which have 

 from the first been backward in increase in thickness, are split off from the adjoining 

 main segments on both sides, or remain connected with one, according as the- two broad 

 medullary rays adjoining them, or only one of them, take part in the extension of 

 parenchyma. Also the four bast-plates, or their parenchymatous portions, undergo a 

 process of widening: but tliey are again narrowed, since the split off and superseded 



