48 



stricted parts of the stems have lost their ability to grow. In 

 Melianthus however which forms periderm within the cast as outside 

 of it, except that its formation is a little delayed within the cast, 

 the xylem parenchyma that is formed before the death of that part 

 of the cortex outside the periderm remains thinner-walled than the 

 cells formed subsequently. The death of the cortical cells releases 

 the whole pressure of the cast. In Vicia the same result has been 

 brought about by removing several casts after an application of 

 several weeks. In these cases also the elements of the inner part 

 of the xylem zone have remained thinner-walled than those formed 

 subsequently to the removal of the cast. 



De Tries found that under pressure the number of vessels pro- 

 portionate to the other xylem elements formed was reduced. In the 

 present researches the like can be proved true for Melianthus only. 

 But the use of casts is not favorable to the study of the question, 

 since there is generally too little growth within the confined part 

 to allow one to judge whether the proportion between number ot 

 vessels and of other elements has changed or not. 



The proportion of phloem to xylem cannot be seen to change 

 in the part within the cast. The result is therefore that there is 

 but little phloem produced in that position. 



5. Changes outside the casts. 



The quite general effect in inducing a resting period in young 

 plants by the application of casts has been given on page 36. Other 

 effects not so general are indicated at the beginning of the description 

 of experiments for each plant species. 



One other feature has presented itself in the plants Cucurbita, 

 Althaea, Vicia, Dahlia and Ricinus. Always in all that part of the 

 stem below the cast the development is weaker than that above. 

 The thickness of stem is less because the activity of the cambium is 

 less. In the 5 plants mentioned 4 are those that have grown well 

 and for a long time within the casts. Melianthus is the only other 

 plant that has thrived and grown for a long period within the cast, 

 and in this the early death of the cortex soon made the cast inef- 

 fective. Thus it is probable that the diminished growth below the 

 cast would be general. 



Neither the presence nor the absence of a weight can be ascribed 

 as the cause of this phenomenon since it appears in cases where 

 the stem below the cast bears the whole weight of gypsum and stem 

 above , and also in cases where the weight of both these parts is 



