1915] 



MERRILL DISTILLED WATER 471 



the full 



growth, plants grown the entire period in renewed full nut- 

 rient solution. 



Plate 13 fig. 2 shows first (Nos. 1 and 2) the contrasted 

 effect of renewing and not renewing the full nutrient solution. 

 The remaining 8 cultures of the plate show the effect of 

 renewing and of not renewing both the distilled water and 



nutrient solution. In cultures 3-10 the comparison 

 should, of course, be made between the alternating numbers for 

 the distilled water effect (renewed or not renewed), and be- 

 tween successive numbers for the effect of the renewal or the 

 non-renewal of the full nutrient solution. While the culture 

 represented by No. 7 of the plate gave greater growth than 

 did No. 9, that excess was probably due to the individual hardi- 

 hood of two plants. It is seen that a much more uniform and 

 desirable growth was made by the plants of No. 9. 



An interesting point in connection with the horse beans is 

 that 16 days after setting up the series the tips of those 

 plants still in distilled water were more or less blackened, 

 probably as a result of enzyme (oxydase) action, and many 

 of them were considerably inrolled. Such conditions were 

 entirely absent from the cultures in full nutrient solution at 

 that time. When the affected plants were later placed in 

 full nutrient solution there was a gradual recovery from the 

 blackening of the leaves, and this recovery was greater in 

 the case of those cultures in which the distilled water had 

 been renewed than in those in which it had not been renewed. 

 Twenty days later Nos. 3 and 4 were in very much better 

 condition than Nos. 1 and 2. There was much less blacken- 

 ing, some leaves not being blackened at all. The general 

 height of the plants in Nos. 1 and 2 was 1^-2^ inches ; and in 

 Nos. 3 and 4 it was 2£-4 inches. A very noticeable feature 

 at the end of the experiment was the condition of the medium, 

 that of Nos. 3 and 4 beincr of course clear while that of Nos. 1 



and 2 was milky, turbid, and opaque, indicating abundant 

 fungous and bacterial action, a condition further emphasized 

 by the hyphal threads and gelatinous coating on the roots. 



The roots of the plants in Nos. 3 and 4 were also in much 

 better condition at the end of the experiment than were those 



