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pièces are half-cylinders. There remains usually more of the tissue 

 of the stem on one side than on the other. The process of forma- 

 tion of the cavitj' is dépendent on the amount of substance in the 

 half-cylinder. 



1. I will describe the process first in those cases in which 

 one pièce is bigger than the other. 



In the course of a few minutes one can see ') in the living 

 mater ial that the two longitudinally cut-edges form new walls on 

 each side which gi"ow towards one another. The inner edges of 

 the new wall cume togetber first in thuse régions where they were 

 less widely separated at the beginning. A suture is formed along 

 the line of meeting of the edges. The old cavitj' exposed by the 

 opération is closed by the union of two walls which form the clo- 

 sing membrane. 



In many cases, not in ail, I could see in the course of clo- 

 sing of the longitudinally-cut stems a circulation of the fluid within 

 the two walls that were closing in. This circulation takes 

 place within the enlarged swollen edges ofthe half- 

 cylinder and not in the cavity. After formation of the clo- 

 sing membrane the circulation can be seen in the united new walls 

 along the line of suture. This circulation is in the beginning very 

 slight, but becomes later more distinct. When the closing of the 

 cavit}- is finished, i. e. when the edges are united and the closing 

 membrane is formed, the circulation disappears in the tissue around 

 the suture and can be seen soon afterwards 

 in the closed central cavity of the stem. 



There are many difficulties in deter- 

 mining in the living material where the 

 first preliminary circulation develops. The- 

 refore I was induced to study it by means 

 of microscopical sections. The material was 

 fixed at intervais of a few minutes after 

 the opération. 



In the earliest stages the formation of the walls (fig. 2. wj 

 along the whole length of the jDiece can be seen. I could recognize 

 by direct observation of my sections that the wall in the earliest 



Fig. -1. 



My observations where carricd eut with a hiuocular microscope of 



Greenough. 



