STUDY OP THE GENICULA OF CORALLINE. 27 



By careful study of the shape, position and the length of the cells 

 of the genicula, the writer arrived at the conclusion thai the genicula 

 are transformed from the zone or zones of the matured periclinal 

 cell. 



In normal cases the cells sharing the formation of a geniculum 



are limited to the medullary cells. An exception is the genicula of 

 Amp. stelligera and its allied species. In these species the long fila- 

 mentous genicula are formed of several zones of the medullary cells, 

 generally much disturbed in the cellular arrangement. These genicula 

 are coated with cortical layers from the beginning of their formation. 

 In these species the cortical layers around the zonal cells play an 

 important part in giving rise to the primary genicula of the whorly 

 ramules. 



Another example of a geniculum with cortical layers is found in 

 certain species of the Eurytion. In this, the greater part of the 

 overlying cortical layer is dropped off in the process of the genicular 

 formation, which is described below ; but those cortical cells closely 

 adhering 1 to the genicular cells remain as such. These cortical cells 

 have similar characters with the genicular cells in every way and last 

 as long as the genicula exist. 



The primary geniculum of a ramule in Amp. aspergillum^ Amp. 

 valonioideSj etc. is Apparently transformed out of the cortical layers. 

 These are, as a mutter of fact, built up by a similar process as that by 

 which the primary geniculum of the main stem started from the 

 incrustation. The primitive stage of the ramules is a mammilary 

 process on the surface of an articulus. It is built up with a number 

 of layers of globular or rectangular cells not distinguishable from other 

 cortical cells. As the process elongates upwards by the intercalary 

 growth of the cells of one or more layers, the geniculum is transformed 

 from one of the elongated cell layers. The cortical layers, at least the 



