30 



were 6 cm in length, remaining about the stems for 5 or 6 weeks, but 

 produced no decided changes internal or external. Of the 7 stems 

 put into gypsum casts, 2 had then but 3 internodes above the earth 

 and therefore were not hollow, while the other 5 were older shoots 

 and were certainly hollow when the casts were applied. Since the 

 increase in thickness in the stem is extremely slow in the older 

 internodes, the casts were in all cases put around the highest exposed 

 internode or the 2 highest. The two shoots about which the casts 

 were placed supposedly before the cavity was present, showed cavity 

 within the part in the cast when examined some weeks afterward. 

 All 7 plants may then be considered as forming one series of experi- 

 ments. None of them seemed to suffer in any way from the effect 

 of the cast. 



Instead of considering the different individuals according to the 

 length of the period under which they were under experiment, it 

 will be better to take them up in the order of their development 

 subsequent to .the application of the casts, since the amount of growth 

 is not graded to the length of time. 



1. The plant which on examination showed the least development 

 was in the cast for 4S days, in that r^eriod having added but 2 inter- 

 nodes. The position of the cast was marked by a decided constriction. 

 A general movement of cells toward the centre had taken place, since 

 pith, bundle and cortical elements were radially elongated. Pith and 

 cortical cells were smaller than outside the cast. The number of 

 secondary elements in a bundle below the cast was greater than that 

 within, and greater within the cast than above, indicating that the 

 pressure had not been sufficient to reduce noticably the multiplication 

 of cells. The increase in thickness of cell-wall has been decidedly 

 affected. Below the cast is a band of thick-walled secondary xylem 

 cells averaging S in a radial row, and outer pith-cells are thick-walled 

 and lignified. Above the cast a zone of thick-walled pith, 2 cells in 

 width, is shown as well as a group of thick-walled cells capping the 

 inner end of each primary bundle. Within the cast are only thin- 

 walled cells. In the last position the mechanical tissue would nor- 

 mally be considerably in excess of that above the cast. The number 

 of cells in a radial row in the pith number above and below the 

 cast 24, within 2S. 



2. This shoot being next to the foregoing in point of develop- 

 ment, was one of those having the cast applied when there were 

 but 3 exposed internodes above the earth. It has grown well and 

 added 3 internodes. The cavity found within the cast was very 

 small, — the living pith pressing a few cell-remains together in the 



