CLOSURE OF LONGITUDINALLY SPLIT TUBULA- 



RIAN STEMS. 



ALICE M. BORING. 



My work was carried on under the direction of Professor T. 

 H. Morgan and Dr. N. M. Stevens, for whose suggestions and 

 criticism I am deeply indebted. 



The rapid closure of the cut edges of pieces of the stem of 

 Tnbularia which have been split longitudinally, has been studied 

 by Morgan and by Godlewski. The latter has published the 

 results of his observations in two recent papers. Godlewski 

 worked with Tnbularia mcscuibryantlicnnivi, found at Naples, 

 while my own work has been on Tnbularia crocea, from Wood's 

 Hole, Mass. The method of closing in this form appears to dif- 

 fer in a number of points from that of Tnbularia mesembryan- 

 themnin described by Godlewski. Material that had been col- 

 lected by Professor Morgan during the summer was sectioned and 

 studied. The conclusions drawn from this work were then veri- 

 fied on fresh material, of which sections also were made. The 

 study of the living material, however, is not very satisfactory, as 

 it is possible to see so little of what is going on. The circulation 

 of the fluid inside of the open tubes and the gradual stretching 

 across of the membrane, are all that can be seen clearly. 



The splitting was done with a pair of fine scissors. The ma- 

 terial was killed and fixed in corrosive acetic. Somewhere in the 

 process of preserving, probably in the alcohols, the ccenosarc 

 shrinks and loosens from the perisarc, which keeps its former 

 size and shape. This makes it difficult to study their relation to 

 each other in the closing process. The tissues of the ccenosarc 

 are well preserved by the corrosive acetic solution and can be 

 studied easily. The sections were stained with Delafield's hsema- 

 toxylin, followed by picric alcohol, according to the method of 

 Stevens ('01). The picric alcohol stains the granules in the 

 endoderm cells bright yellow, and thus makes the difference 

 between ectoderm and endoderm cells distinct. 



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