26 



rise to a narrow band of secondary tissue. The bundles had in- 

 creased greatly in size, the vessels in an average bundle now num- 

 bering 40 or 50, while in each group of phloem were 10 to 20 thick- 

 walled bast cells where none had existed 33 days before. In the 

 normal stem and also in the one in gypsum above the cast was a 

 cavity in the pith more than y 3 the width of the stalk; the remain- 

 ing pith- cells had enlarged and those lying next the bundle-ring 

 had become thick-walled and lignifled. Below the cast, this being 

 in the epicotyl , there was no cavity and no thick-walled pith- cells, 

 — a perfectly normal condition. 



Section taken through that part of the 3rd internode that was 

 within the cast, should be compared with the sections described as 

 taken above the cast rather than with those below. Observations on 

 the structure of the encased part of the 3rd internode teach that 

 little development has taken place within 33 days. The cortex 

 shows its cells with smaller intercellular spaces than before the cast 

 was applied, and with greater radial elongation. Cambium is no- 

 where to be seen between the bundles. In the phloem are no thick- 

 walled cells. In the xylem, instead of 2 or 3 lignifled elements in 

 a bundle as 33 days ago, are 40 or 50, — partly vessels and partly 

 wood-parenchyma. To form this group of lignifled elements the 

 weak cells there present 33 days ago have grown but a little in 

 size. The cells have apparently enlarged, become somewhat thick- 

 walled and lignifled. These elements are, it is to be noted, of 

 smaller size than they occur in normal growth. The pith is solid 

 and all its cells are living. The only change that has taken place 

 here since the cast was applied is in the closing of the intercellular 

 spaces. 



At the upper limit of the cast there is an excessive development 

 of mechanical tissue in the xylem and in the outer part of the pith. 

 Above the surface of the cast where the stem enlarges from the 

 constriction there is more of this thick-walled tissue than anywhere 

 else in the stem. Below this surface and hence within the con- 

 striction, the amount of such tissue is less, but still much more than 

 well within the cast. Cells with the same ralative position and the 

 same size as those with very thin walls l cm below the surface of 

 the cast, have walls increasing in thickness as the upper limit of 

 the cast is approached. 



3. 43 days after application of cast. Above and below the cast 

 the normal development had gone on in the tissues. The large 

 intercellular spaces in the cortex had grown to tangential splits 

 extending the length of many cells, the spaces being bounded by 



