MOVEMENTS OF GROWTH. 3(37 



consequently take place. The shortening is then gradually fixed 

 by growth. It is now of special interest to study accurately this 

 contraction of the root resulting from turgor, since it is the indis- 

 pensable condition for the subsequent shortening, to be rendered 

 permanent and irreversible by growth. 



We sow seeds of Carum carvi in good garden earth in the open, 

 in summer, and let the plants grow till they are two to three 

 months old. I sowed at the end of July, and used the material 

 for investigation at the end of October. When the experiments 

 are to be made we remove the plants from the soil, at once cut off 

 the tops, so as to provide against excessive loss of water from the 

 roots owing to transpiration by the leaves, bring the roots into the 

 laboratory, and after washing and drying them remove their 

 secondary roots and the thin terminal portion. It is now 

 necessary to provide the roots with ink marks, and to do this we 

 lay each of them in turn on a sheet of cork along one half of 

 Avhich. is fastened a second sheet of cork, whose thickness is about 

 the same as that of the root to be operated upon. The root is 

 placed against the edge of the upper sheet of cork, and fixed there 

 by means of needles, which are stuck into the lower sheet close up 

 to the root. The ink lines are finally painted on at definite 

 intervals with the help of a brush and a millimetre scale. In my 

 experiments with Carum roots, which at the upper end, i.e. at 

 the morphological base, were 6-9 mm. in thickness, the distance 

 between the two marks was 70-100 mm. The roots are next 

 placed in fiat glass dishes filled with water.* If now, after a 

 certain time, we measure the distance of the marks from one 

 another, at intervals of, say, 2, 4, 24, 2 x 24, and 4 x 24 hours, we 

 find that they get nearer and nearer, till finally no further 

 contraction takes place. The extent of the contraction is consider- 

 able. In different cases which I observed it reached at the end 

 of twenty-four hours 2' 5 to 4*0 per cent. 



If we dry the contracted roots and plasmolyse then by immer- 

 sion in common salt or Potassium nitrate solution, it is found that 

 while becoming flaccid they have, even after a few hours, elongated 

 considerably. This elongation, however, stands in the closest 

 relation with the contraction accompanying the increased turgor 

 of their root cells due to absorption of water. 



* It is advisable before placing the marked roots in water to let them stand 

 for a few minutes in moist air, so as to make sure of the ink adhering. 



