124 SHORTENING OF BOOTS. [CH. V 



■water should be added. The results of the increased 

 turgescence so produced vary with the material employed ; 

 in the case of Elder and Sunflower the pith begins to 

 shrink, i.e. diminish in transverse diameter; Rhubarb-pith 

 increases and afterwards diminishes; while Impatiens 

 increases but does not diminish. 



(156) Change in tangential dimension. 



Cut with a dry razor sections (such as would be con- 

 sidered very thick for microscopic purposes) of a fresh 

 dandelion-stalk or (in winter) of the hollow hypocotyl of 

 Ricinus. Place the rings, so prepared, on a _ glass plate, 

 and with a scalpel divide each at one point. The divided 

 rings are now placed in water, when their curvature is 

 found to increase, the curling inwards being due to the 

 shrinking in tangential direction of the turgescent tissue 

 forming the inner part of the ring. 



(157) De Vries' eooperiment on the shortening of roots. 



In the roots of certain plants a phenomenon has been 

 observed by de Vries' which seems to be of the same 

 character as those described under experiments 155 — 56. 

 The roots shorten along their longitudinal axes when tur- 

 gescence is increased, and lengthen when turgescence is 

 diminished, e.g. by immersion in 5 per cent. NaCl. 



De Vries describes the phenomenon in Carum, Dip- 

 sacus and other plants. 



Full directions are given by Detmer^ for observation 

 on the roots of young (2 — 3 months) plants of Garwm 



1 Landw. Jahrb. ix. 1880. 

 ^ Praktikum, p. 248. 



