ROOT HAIRS AND GROWTH 



365 



of taking observations, namely, between 

 ix and 16 hours after insertion. 



Measurements of the length of 8 to 16 

 root hairs on each root were made at ten 

 minute intervals during three hours begin- 

 ning 13 hours after insertion of the root in 

 the solution. The root hairs measured 

 were such as appeared after ten hours 



microns 



shown (14) that they will not elongate in 

 distilled water during the period studied. 

 In fact few root hairs are produced after 

 immersion in pure water. Inasmuch as 

 the different molar concentrations of 

 calcium hydroxide differ in the degrees of 

 their alkalinity, the constitution of these 

 solutions may be determined either volu- 









100 









0.020 a 0.008 



0.000 



80 



/ /^ ^0— - 





60 ' 

 40 



/ y*0.028 J\/ \J 





f^~^LL_ 1 0.060/^ / \ 





20 



/ L^ / I 0.120 







f L^/ x 





10 



11 



12 pH 



Fig. 5. Graphs Representing the Rate of Root Hair Elongation of Collards in Solutions of Different 

 Molar Concentrations of Calcium Chlorid, Plotted along the Scale of Hydrogen Ion 

 Concentrations. The Graph Labeled o .000 is for Calcium Hydroxide 



immersion, that is, after the root had be- 

 come entirely adjusted to the solution. 



The determination of the rate of elonga- 

 tion of root hairs in calcium hydroxide is 

 of interest because it is the simplest solu- 

 tion in which they will grow at all. It is 

 highly interesting, therefore, to find that 

 in this simplest solution they have been 

 found to grow faster than in any other 

 medium so far studied. It was definitely 



metrically or colorimetrically. Both 

 methods were employed. The initial 

 study with calcium hydroxide was made in 

 192.6 (14), and the study was repeated the 

 next year (2.0), completely confirming the 

 previous results. 



It was found that the rate of elongation 

 rises from zero at pH 7 (fig. 5), neutrality, 

 to a first optimum at pH 8, and then drops 

 to a median minimum at pH 9.0, rising to 1 





