346 The Effect of Fotassiinii Salts on Dactylis glomerata 



The most striking feature in the progress of wall thickness in the 

 material supplied with full minerals (Fig. 6) is the sudden increase 

 between June 8th and June 15th. During the periods both preceding 

 and following this increase the thickness diminished by an amount 

 which, though slight, seems to be outside the limit of variation. 



The corresponding changes in the diameter of the lumen are shown 

 in Fig. 7. On May 15th the cells were large and little differentiated, but 

 by May 31st the mean diameter had decreased by 7-5/x. During the 

 following week (June 1st to Jime 8th) an expansion of the cells occurred 

 — the lumen increased while the wall thickness diminished. This increase 

 in the lumen was not observed in any other material excef)t that from 

 Plot 10, where it will be remembered no potash was supplied although 

 ammonium salts were given as a source of nitrogen. It does not, there- 

 fore, appear to be the result of supplying potassium salts to the plant. 



As already explained, the ratio of wall thickness to lumen may be 

 taken as a measure of mechanical strength of the individual cell. For 

 purposes of convenience the ratio has been inverted. Fig. 8 shows the 

 progress of the ratio of lumen to wall in Plot 7 material which followed 

 closely that of the lumen diameter. The course of the curve indicated 

 that the mechanical strength of the cells increased considerably during 

 the season but that the increase was not uniform throughout, and on 

 one occasion, between June 1st and June 8th, a decrease occurred. 

 Reference to the weather curv^es shows that during this week there was 

 moderate rainfall after a short period of drought. This might account 

 for the stretching of the cells, but does not explain the fact that the 

 same thing is not seen in material from the other plots. The thickening 

 and recovery from this weakening influence during the ensuing week 

 must be emphasised. 



B. In metaxylem vessels. 



Plot 7. Xylem. Complete mineral manures. 



Date May 16th May 31st June 8th June 15th June 26th 



WaUa 1-92^1 2-16/i 1-93m 204m 216/* 



Lumina 24-6/i 269^ 29-6m 31-45m 27-8m 



Ratio 93-41 14-44 1619 15-56 13-38 



As may be seen from the curve in Fig. 9 there was very little change 

 in the wall thickness in the material receiving potash throughout the 

 summer. The slight apparent drop between June 1st and June 8th was 

 possibly due to experimental error, but is too great to be dismissed as 

 such. It occurred during the same period as the similar decrease in the 

 sclerenchyma walls. 



