The table shows that in this typical case, the deviation from the 

 means does not exceed 5 per cent, and that it is possible to obtain 

 significant differences between the means on different dates, and, as 

 will be seen later, in material from different plots. In this case the 

 differences between successive measurements were significant until 

 June 15th, but between June 15th and June 2()th they were too small to 

 be considered. 



Results. 



The sclerenchymatous zone consists of rather small isodiametric 

 cells, with heavily hgnified walls. In all stages examined the living 

 protoplast was actively secreting cell- wall material, and the walls were 

 therefore becoming thickened as the season progressed. 



The xylem vessels on the other hand were no longer Uving cells ; it 

 is, therefore, impossible that new wall material should be deposited. 



Development under Normal Conditions of Potash Supply. 



(Plot 7, full minerals supplied.) 



A. //( sderenchyina. 

 The rate of change, both in wall thickness and in the diameter of 

 the lumen, is by no means regular. On May 16th, when the material 

 was first collected, the mean wall thickness was 1-88jli. The stems at 

 this date were very immature, and not more than two or three centi- 

 metres long. The degree of differentiation varied considerably between 

 individuals at this early stage; two or three days start was enough to 

 allow lignification to be well ahead in some specimens. In addition, as 

 the sections did not take the stains readily, accurate measurement 

 under the high power used was extremely difficult. In consequence, 

 less reliance can be placed on this set of measm-ements than on those of 

 a later date, but they are sufficiently different from those of the suc- 

 ceeding set to show that a considerable change has taken place. 



" Plot 7. Sclerenchyma. Complete mineral manures. 



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



Walls 1^88±-09m 2-81±-U/i. 2-39±-06^ 506±10^ 4^27±^13m 



Lumina 15-6 ±^27m 8-1 ±^23m 101 ±-32^ 7-5 ±-21m 7^8 ±^22/t 



Ratio 9-37 3-22 4-3 1-57 212 



