18 ART. 14.-K. YENDO: 



the illustrations of " Etude Phycologique "° and " Sur les Coral- 

 lines " 2) no precise point about it is given. 



To begin with, we will treat of the unizonal geniculum ; that 

 is to say, a geniculum built up with a single zone of periclinal cells. 



The genicular cells are long filamentous cells, varying in the 

 proportion of their length and their diameter according to whether 

 they take the middle or the peripheral position in the geniculum. 

 The diameter of the cells is constant or nearly constant in a species. 

 The part at both ends which I have called " extra-genicular portion " 

 has mostly a different diameter from the genicular portion proper. 

 The diminishing or the increasing of the diameter occurs abruptly at 

 the critical points between the two portions. 



In regard to the length of the filaments, we find that it varies 

 according to the species ; but it is always several times, often more 

 than twenty times, as great as the breadth. We can not tell the 

 proportional length by the mere external appearance of a geniculum. 

 This is owing to the relative size of the circurn genicular cortex. 



In the cross sections of the ^enicula we find the cells more or 

 less polygonal from mutual compression. The cell rooms are 

 comparatively narrow and mostly roundish polygonal. 



Staining with colouring materials, we can easily perceive the 

 lamellar structure of the cell wall in the genicular cells. The 

 comparison of the properties of the wall with those of the articular cells 

 is highly interesting. In the present paper it is not the aim to give 

 the details of the microchemical properties of the cell wall, but some 

 remarkable features we shall not fail to point out hereafter. 



1) Bobnet et Thoret ; PI. L-I.I. 



2) Decaisne: PI. 17. fi«'. 5 





