348 The Effect of Potassium Salts on Dactylis glomerata 



In each, set, however, one anomalous plant occurred. One section 

 from Plot 7 showed well lignified sclerenchyma, while one from Plot 8 

 was hardly differentiated. These plants had been influenced by some 

 other factor and for this reason their measurements were omitted from 

 the mean values. 



The wall thickness in Plot 8 material is shown in Fig. 6. 



Between May 16th and May 31st it decreased by 1-2 /x, while during 

 the same period an increase was observed in the case of plants which 

 had received potassium manures. It is difficult to account for this fall, 

 which cannot be due to stretching, for at the same time the lumen has 

 decreased. From this date onwards the thickness continued to increase, 

 until June l.jth, when maximum development was attained. The wall 

 thickness throughout, with one exception (on May 31st), was greater 

 than in Plot 7 material; this difference was most marked in the very 

 young stages. 



Eeference to Fig. 7 shows that the lumina in absence of potassium 

 salts were smaller than where these were applied, with the exception of 

 those in stems obtained on May 31st. The general tendency to additional 

 strength of the cells was shown here by Plot 8 material in the smaller 

 diameter of the lumen as well as in the greater thickness of the walls, 

 and the reversal of this general tendency on May 31st was again exem- 

 plified. 



Throughout the whole period there was a slow decrease in the lumen, 

 except during the last ten days when a slight increase occm'red, and 

 during the first week in June when there was no change. 



In Plot 8 material an increase in the ratio of lumen to wall occurred 

 during the first period (May 16th — May 31st) due both to the rise in wall 

 thickness and the decrease of the mean lumen diameter (Fig. 8). After 

 this date the ratio fell slowly till Jinie 15th, and thereafter remained 

 constant till June 20th. 



The ratio was below that found for Plot 7 material, except on 

 May 31st. From June 8th onwards, however, the difference was slight. 

 This comparison indicates that where potassium salts have been added 

 (Plot 7) the mechanical strength, as measured by the reciprocal of the 

 ratio of lumen to wall, was reduced, especialh^ in the early stages of 

 growth. On May 31st, however, this conclusion does not hold; for some 

 reason the plants treated with potash had thicker walls and a smaller 

 lumen than where it had been omitted. 



The wall thickness in Plot 8 as shown in Fig. 9 again remained fairly 

 steady throughout the season; from May 31st onwards a very slight 



