340 ROOT CONTRACTION 



The warped and altogether disorganized condition of the epi- 

 dermis and "hypodermal" layers in the contracted roots of 

 Cooperia Drummondii may be comprehended by study of the 

 tissues represented by the blackened areas in the figure, section 1. 



It seems safe to accept these facts: (1) roots do shorten; (2) 

 the parenchymatous tissues of the root are the seat of activity; 

 (3) the cork and the vascular trace are passive; (4) the cork is 

 ultimately crushed ; (5) there is a region where one can see wrink- 

 lings and measure shortening, a second region where no wrink- 

 lings are visible yet one can measure shortening, and an un- 

 changed region (Rimbach) ; (6) in dicotyledons the trace becomes 

 visibly curved inward and outward in a wavy fashion, while in 

 monocotyledons the vascular bundles remain practically straight 

 (de Vries). 



What remains to be determined in regard to root contraction 

 constitutes a problem of botanical research as yet unsolved. 

 We may hope that some worker with an interest in morphology 

 as. well as physiology may master this problem by a study of 

 serial sections of young roots and a consideration of the physical 

 relations of turgor and biochemical alterations in the protoplast 

 and cell membrane. 



