338 ROOT CONTRACTION 



Rimbach discusses root contraction as it occurs in Colchicum 

 autwnnale, 3 Arum maculatum 4 and Allium ursinum. 5 He found 

 that in the c?se of naturally deep-set bulbs of Allium ursinum 

 a depth of 10 to 15 cm. was attained after several years by the 

 contraction of the roots. In the explanation as to how contrac- 

 tion in roots comes about he states that, while the root tip holds 

 firmly to the earth particles, the endodermal cells contract longi- 

 tudinally as a result of a tendency to lengthen radially and tan- 

 gentially, which results in the contraction of the root. The bulb 

 yields to this pull, which results in the contraction of the roots, 

 and is gradually placed more deeply in the ground with each new 

 set of roots. Even the upward development of the shoot, where 

 each successive scale is formed at a slightly higher level, does 

 not counteract entirely this downward movement of the bulb. 

 Therefore the bulb is continually placed more deeply in the soil. 



In Arum maculatum, Rimbach 4 explains, the active portion of 

 the root consists of the cells directly below the epidermis and the 

 ' 'hypodermal layers." These cells shorten in their length as 

 much as one half and their radial walls lengthen somewhat. The 

 vascular bundles and their accompanying cells are not active. 

 However, the latter respond sufficiently to the vertical pressure 

 caused by the shortening of the parenchymatous cells just out- 

 side them to show regular wrinklings along their walls, and the 

 tracheal tubes themselves shorten between the rings. 



Rimbach's careful observations and well chosen biological ex- 

 periments are not supported by his theoretical conclusions. Be- 

 cause he has accurately noted that endodermal cells lengthen 

 radially, he proceeds to state that they shorten longitudinally and 

 therefore the whole root contracts with the result that the bulb 

 is set more deeply into the ground. All other tissues are passive, 

 yet they must be shortened in the shortening of the whole root. 

 Without sufficient morphological proof Rimbach claims that the 



3 Rimbach, A. Biologische Beobachtungen an Colchicum autwnnale. Ber. 

 deuts. bot. Ges. 15: 298. PI. 12. 1897. 



4 Rimbach, A. Ueber die Lebensverhaltnisse des Arum maculatum. Ibid. 15: 

 178. PI. 5. 1897. 



6 Rimbach, A. Lebensverhaltnisse des A Ilium ursinum. Ibid. 15: 248. PI. 8. 

 1S97. 



