METHODS OF EXPERIMENTS. 19 



mini ;ind placed in Iseakers containing the solution, the tips of the 

 roots heiiiii- iinmersed in the liquid. One rootlet of each seedling was 

 marked with India ink 15 mm. from the apex, Avhich should include 

 ])ractically all of the rapidly growing zone. The amount of elonga- 

 tion during a given period could thus be determined, and this is the 

 best means of knowing whether the root has been actually killed. 

 Unless the concentration of the solution be far above the toxic limit 

 the root does not become flaccid, as is the case with lupines and some 

 other seedlings. After the roots were marked with iiidia ink the seeds 

 were carefully hooked on to the glass rods prepared for that i:)uri)Ose. 

 As much of the root was immersed in the solution as was possible 

 Avithout allowing the seeds or rods to come in contact with the liquid. 

 In all cases the entire length of the marked zone was immersed. The 

 length of the portion of the root in the solution depended, of course, 

 upon the total length of the root. It might at first glance seem that a 

 variation in this respect could alfect the result of the experiment, some 

 roots having a larger surface exposed to the solution than others ; but 

 it is believed that the large number of seedlings used in each experi- 

 ment practically eliminated this source of error. 



All cultures were left in the solution twenty-four hours, when they 

 were taken up and the amount of elongation of the marked portion of 

 the root was measured and recorded. They were then transferred to 

 a beaker containing hydrant water and allowed to remain there for 

 another twenty-four hours, when tlie^y were taken up and the elonga- 

 tion again measured. The radicles Avhich made an additional growth 

 the second twentv-four hours in the hvdrant Avater over the growth in 

 the first twenty-four hours in the salt solution were considered to have 

 survived in the solution and were thus recorded. Those making no 

 additional growth the second twenty-four hours were considered dead 

 and recorded in this way. Coupin and others have intimated that 

 twenty-four hours is not sufficient to kill the plant. This objection is 

 set aside by the consideration that only the death of the apex of th(5 

 root is regarded in these experiments and not the point at which the 

 whole plant succumbs. The object of this work is merely one of com- 

 parison of the effect of a solution of given concentration, during a 

 definite period of time, upon different varieties. Whether this effect 

 is expressed in the death of the whole plant or only that of a single 

 organ is immaterial. 



Control experiments Avere carried on every day, one in hydrant 

 water and one in distilled water, both under conditions identical 

 with those in the salt solutions. The results in hydrant water have 

 been uniform from day to day and in only a few cases were they 

 proved unsatisfactory. In such cases the whole series was discarded, 

 the inference being that some unfavorable condition (of temperature, 

 for example) had interfered. 



