136 SHORTENING OF ROOTS. [CH. V 



(156) Change in tangential dimension. 



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

 sidered very thick for microscopic purposes) of the fresh 

 scape of the dandelion {Taraxacum) 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 experiment 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 solution. 



De Vries describes the phenomenon in Carum, Dipsa- 

 cus and other plants. 



Full directions are given by Detmer- for observation 

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

 carvi. If suitable material is wanting for following out 

 Detmer's instructions, it is generally possible to find roots 

 in which shortening has already occurred, and which are 

 remarkable for their wrinkled exterior. The roots of 

 hyacinths grown in water show the phenomenon well. 



1 Landiv. Jahrb. ix, 1880. 



2 Praktikum, p. 248. 



