49 



removed by external support. It is possibly caused by poor nutrition, 

 the transport from above downward being intercepted by the small 

 amount of conducting tissue within the cast. 



IV. RESULTS. 



From the foregoing experiments, the following results have been 

 obtained : 



1. When all the usual conditions of growth are present, meristem- 

 atic and young tissue, by a mechanical force resisting extension, 

 may be held for an undetermined period in a condition amounting to 

 rest without losing their functional capability. 



2. The life-period of all cells may be prolonged by preventing 

 their full extension through mechanical resistance. 



3. Organs in which the death of cells accompanies the cavity- 

 formation during primary growth will remain longer without dead 

 cells if the extension of the stem is checked; and the earlier the 

 extension is checked the longer will be the life-period of the cells. 



4. Under pressure all elements will finally mature at a smaller 

 size than normal. 



5. A mechanical resistance so applied as to prevent enlargement 

 and reduce tension will lessen the formation of mechanical tissue. 



6. A mechanical resistance so applied as to prevent enlargement 

 but to increase tension will increase the amount of mechanical 

 tissue. 



7. Of mechanical tissues growing under pressure the hard bast 

 will remain longest thin-walled. 



&. When the resistance from the centre . is not great and the 

 plant cannot extend radially, the tissues will grow toward the centre. 



9. When a segment of a stem through mechanical resistance 

 is kept from enlarging by secondary growth, the part of the stem 

 below the constriction will in many cases grow less rapidly than 

 that above. 



