34 



an entirely living pith within , but a hollow one above and below. 

 Within the cast also the cells had remained smaller and had not 

 multiplied to such an extent as above and below. The cortical cells 

 were elongated radially and the vessels were distorted. There were 

 no thick-walled cells within the casts, but all of the branches showed 

 mechanical tissue below and 2 of them above the casts. Such mechan- 

 ical cells were the hard bast and the xylem parenchyma. 



2. In the second series 6 young plants had parts of the stem 

 enclosed in gypsum , — 5 of them receiving the casts around the 

 middle of the hypocotyl before the cavity had appeared, and one 

 around the epicotyl after the cavity was there present. 



The first plant in this series was taken for examination 30 days 

 after application of the cast, the cast being about 3 cm in length and 

 occupying the middle of the hypocotyl. The diameters of the stem 

 below, within and above the cast were respectively 13 : 9 : 12. The 

 diameters of the pith in the 3 positions were nearly equal, that below 

 the cast being a very little greater than within, and that within 

 being a little greater than above. The width of the cortex made 

 more than half the difference in the diameters given, and next to it 

 in amount of variation stood the bundle-ring. The cambium-zone 

 was present throughout the hypocotyl before the latter was encased. 

 During the 30 days , the secondary tissue that had arisen from the 

 cambium within the cast did not exceed 2 or 3 cells in the radial 

 direction. The changes that had taken place within the cast con- 

 sisted almost solely in the addition of these few secondary cells and 

 the thickening of walls of vessels, xylem-parenchyma and hard bast 

 that existed in the thin-walled condition and in about the same size 

 of cells before the cast was applied. These elements of the bundle- 

 ring are fewer, a little thinner-walled and the xylem elements a 

 little shorter radially than above and below the cast. The room for 

 this very slight growth within the cast has been made by filling the 

 intercellular spaces of pith and cortex. The number of secondary 

 elements including the cambium that can be counted in a radial row 

 are below the cast 12, within 7, and above 11. 



The other 4 plants that received casts about the hypocotyl showed 

 within the abnormal segments, which were from 3 cm to 4 cm in length, 

 the same relations. They had grown after the application of the casts 

 for periods varying from 65 to 100 days. The diameter of the stems 

 in the normal part was from 3 / 2 to 2 times that of the part within 

 the cast. 



In each case the cavity extended downward in the hypocotyl 

 to within a few millimeters of the cast, and below that point was 



