ORGANIZATION AND GROWTH 203 



laria it is an easy matter to diagnose the organ from which 

 a fragment has originated. If such a Bryopsis is laid hori- 

 zontally upon the ground, "the growing stem becomes erect 

 at its tip, the leaf tubules again grow obliquely upward at 

 their usual angle, and the root tubules grow downward into 

 the dark earth." Noll then tried "whether a root could be 

 produced from the tip of the stem, and a new stem from the 

 root tubules." He suspended plants from which the roots 

 had been cut in glass tubes in an inverted position, that is, 

 with the tip downward. When the experiment was brought 

 to a close after some time, 



the tip in a number of plants had greatly increased in length, but 

 instead of growing upward it had grown downward into the sand, 

 was bent, and intimately connected with the grains of sand ; in 

 short, it had been transformed into a typical root tubule. Even 

 the few leaves which had been formed had also grown into roots. 

 Another series of these specimens did not show this transformation ; 

 in these the tips turned upward at an acute angle and returned in 

 their old direction ; they remained stems. 



In regard to the latter point the behavior of Antennularia 

 is essentially different. When the tip is directed downward, 

 its growth as a stem ceases immediately ; never under these 

 circumstances does it bend so as to grow in its old upward 

 direction. 



Further growth can now take place only in so far as the 

 tip continues to grow as a root. In Noll's experiments a 

 tubule which grew upward arose at the upper basal end, and 

 in some cases showed a beginning barbule formation. 

 According to Noll, light is the essential factor in the control 

 of the morphogenesis. 



III. THE ARTIFICIAL PRODUCTION OF A VARIETY OF 

 ANTENNULARIA ANTENNINA 



The main stem of Antennularia antennina is unbranched. 

 In the hundreds of specimens that passed through my hands 



