11 



indicated in the plant earlier examined. The pith within the cast 

 had died nearly out to the bundles without collapsing; hence there 

 was no cavity. The cavity above and below was normal. The inter- 

 cellular spaces in the cortex had been in the abnormal segment com- 

 pletely closed up. The bundles had grown about as large within as 

 outside the cast, but many vessels in the constricted part were flat- 

 tened, not all in the same direction. The normal sclerenchyma 

 sheaths of the bundles were well developed outside the casts ; within, 

 the thick- walled condition was entirely absent. There had apparently 

 been little or no movement of bundles toward the centre. 



The other 2 plants may have had small clefts in the pith when 

 the gypsum was laid around them, but they certainly had no general 

 cavity. The stems above the casts were not a great deal thicker than 

 within. The central cavity was present through the parts in casts. 

 The cortical intercellular spaces were not wholly closed. The bundle- 

 sheaths within the constricted segments showed in each plant slightly 

 thickened cell-membranes, but still much thinner than above and 

 below these places. Because of the very loose tissue lying outside 

 and inside the ring of bundles, the pressure here which had influenced 

 to so large an extent the thickening of cell- walls could not have 

 been very great. 



One of the stems had increased in size outside the cast con- 

 siderably more than the others, and at the upper limit of the cast 

 showed the inner ends of the sclerenchyma sheaths stronger than any- 

 where else in the stem. 



Lamium garganicum L. 



In the stems of Lamium garganicum that have reached a height 

 of several internodes above the soil, the cavity is usually found in 

 the 4th internode from the apex, beginning about the time the cam- 

 bium-zone is completed. The cavity arises from the union of several 

 schizogenous clefts and enlarges lysigenously. 



This plant is little suited to the kind of experiment here made ; 

 for out of 5 about the upper part of whose stems casts were placed, 

 none grew well and only 2 reached a length of several centimeters 

 above the gypsum, the other 3 dying after a period of several weeks, 

 without growing. 



The 2 plants which survived the treatment were examined, the 

 first 24 days, the 2nd 45 days after the casts were applied. They 

 had developed about equally however in these different intervals, and 



