14 



Below the casts the cortical sclerenchyma and the xylem par- 

 enchyma had both thinner walls than above the cast, and conse- 

 quently thinner walls than normally. 



3. Examination after 66 days. 



a. Three plants similar to those just described were treated in 

 the same way but allowed to grow for 66 days. One of them was 

 less developed than the others and probably had no cavity in the 

 hypocotyl when the cast was applied. This younger plant produced 

 above the cast in this time 6 internodes with a total length of 

 10 cm . The other 2 plants had reached a length of nearly a meter. 

 Cavity was present within and without the casts. A record of the 

 histological differences in these plants would be a simple repetition 

 of that for the foregoing 5 plants. One point however should be 

 noted: 2 of these plants showed abnormal swellings above the cast, 

 and sections showed that all kinds of cells had taken part in form- 

 ing this greater thickness. Cortex, pith and cambium were here 

 abnormally active in cell-division. 



b. One very vigorous plant with 5 well developed leaves had 

 its 2nd epicotyledonary internode encased. The plant grew better 

 than any of the younger ones in casts, showed no abnormal swelling, 

 filled the cavity within the constricted segment, and gave the same 

 general results that the others gave. The preexisting cavity gave 

 room for the formation of nearly normal bundles. All thin-walled 

 cells remained smaller than above and below the cast, and thick- 

 walled cells were fewer and weaker. 



In part of the foregoing plants the pith was better preserved 

 within the cast than without, but generally the plants made such 

 poor growth that much could not be decided on this point. 



Althaea tauriensis DC. 



The cavity-formation in Althaea is first indicated by the appea- 

 rance of large intercellular spaces among groups of cells in different 

 parts of the pith. Such groups are separated both in cross and 

 longitudinal sections by intervening tissue composed of more com- 

 pact cells. The mucilage cells of the pith play no especial part in 

 the breaking down of tissue. The large intercellular spaces run 

 together to form clefts, and immediately the bounding cells collapse. 

 Thus there arise in the pith many cavity-islands separated by vigorous 

 looking cells containig a good amount of protoplasm. This condition 

 which does not come into existence till after elongation has ceased 



