19 



here as above and below the cast, the cambium ring is not com- 

 pleted, and the outer pith-cells are not nearly so thick-walled. There 

 can be no question but that the corresponding cells that within the 

 xylem in normal parts of the same stem have become thick-walled 

 are here still in their early thin-walled condition. 



In this plant there was no cavity below nor in the cast and but 

 a very small one above. 



2. Three plants that, when but 3 or 4 internodes in height, had 

 casts placed around the highest exposed internode and part of the 

 next lower one were allowed to grow afterward for 4 months. They 

 had not become strong plants and had reached heights varying from 

 35 cm to 40 cm . The weakness of these individuals is to be in part 

 accounted for from the fact that weak plants were selected for the 

 experiment, since only such have a living pith when they are at a 

 size suitable for application of casts. All these plants showed the 

 stem within the cast from 2 / 5 to 3 /& the diameter above and below; 

 all of them showed the abnormal swelling just above the cast. 



In internal structure all the stems showed cavities above and 

 below the casts but none within, and less multiplication of cells, and 

 less mechanical tissue within the casts than above and below. One 

 showed within the cast in each bundle a small group of hard bast 

 and a few thick-walled xylem parenchyma cells. Between the bundles 

 was a band of thin-walled cells derived from the cambium and con- 

 taining in a radial row 8 cells. Above the cast the thick-walled cells 

 in a corresponding position numbered from 18 to 20. Within the 

 cast the parenchyma cells among the vessels were thin-walled; above 

 and below they were thick- walled. It is quite possible that the most 

 of the thick-walled cells within the cast in the phloem and xylem 

 were present in this plant when the cast was applied; the cambium- 

 zone and its derivatives w T ere certainly then not present. 



A second one of these 3 plants showed much less development 

 within the cast and much less formation of secondary tissue outside 

 the cast than the preceding. The differences however within and 

 without the limits of the gypsum were the same in kind. In this 

 case the plant must have been less differentiated internally than in 

 the preceding when the cast was applied; but a few bundles in the 

 constricted part of the stem showed any hard bast. 



The 3rd plant had above the cast a secondary ring of thick- 

 walled elements from 8 to 10 in a radial row. Within the cast the 

 cambium ring had not been formed, and but for 2 or 3 thick-walled 

 xylem parenchyma cells in each of 2 or 3 bundles, thick-walled cells 

 were entirely wanting. Here was almost a complete suspension of 



2* 



