3<D2 HELEN DEAN KING. 



As was the case in the experiments made by Morgan, the 

 results for corresponding pieces of different stems are far from 

 uniform, and it is not possible to determine what kind of a struc- 

 ture will be produced by a small piece from a given region of 

 the stem. It is evident that the power to form either complete 

 or double structures is present throughout the stem, and just 

 what conditions are necessary to produce certain structures have 

 not, as yet, been fully determined. Morgan has suggested that 

 possibly the factors in determining the kind of regeneration are 

 (i) the smallness of the piece, (2) the differences in the region of 

 the original stem from which the pieces came (this factor had 

 been previously suggested by Driesch), (3) the age of the piece, 

 as the younger the stem the more likely it would be to form 

 incomplete structures. 



According to this set of experiments short pieces, no matter 

 from what part of the stem they are taken, are more liable to 

 produce proboscides than to form hydranths. When the latter 

 structures appear they are usually produced by the more proxi- 

 mal pieces of the stem, the distal end of the stem showing a great 

 tendency to produce incomplete structures. These results are 

 very similar to those obtained by Morgan on Tiibnlaria inescin- 

 bryantlicinitin. 



In order to ascertain whether the double structures that are so 

 often obtained in such experiments are produced because the 

 small pieces of the stem are open at both ends and not because 

 there is insufficient material in the piece to produce a complete 

 hydranth, Morgan tied one end of a short piece with silk thread, 

 and found that, under these conditions, double structures are 

 never produced. Later he planted short pieces of stems in rows 

 in sand so that one end was buried and the other freely sur- 

 rounded by water. In two instances only was a double proboscis 

 formed, in all other cases single structures, either incomplete or 

 whole, more often the latter were produced. 



In repeating these experiments of closing one end of a short 

 piece of the stem of Tubularia in order to ascertain the effect on 

 the kind of structure produced, the following method was used : 

 Shallow, flat dishes were covered on the bottom with a layer of 

 paraffine about one fourth of an inch in thickness, and then, with 



