BOTANICAL SUBJECTS. 331 



XVIII.— THE DISK, THE CITRUS, THE RUTA, AND 

 THE P^ONIA M0UTA:N^. 



The Disk. 



What is the morphological position of what we call in general 

 terms the dish .^ 



Asa Gray defines the disk as a " part of the receptacle, or a 

 development of it, enlarged under or around the pistil." Then, 

 according to its exact position, various names are given to it. 

 " Not rarely," he says, " it divides into lobes, as in Vitis, in Peri- 

 winkle, and most Apocynaceous plants, and in Cruciferae. These 

 are termed glands of the dislr, and, indeed, are commonly glandular 

 or nectariferous. It is not possible by any direct demonstration to 

 distinguish between such productions of the receptacle, which are 

 classed as belonging to the axis, and suppressed or undeveloped 

 phyllous organs, such as stamens, which glands of the disk may 

 sometimes represent." 



This is true, and the reason of it is not far to seek, for there is 

 no mcyrphological difference between the axis and its sub-divisio?is, 

 commencing from the bud-scales and ending in the carpels 

 and ovules. 



Considering that the flower is a shortened branch, the re- 

 ceptacle becomes no other than the central part of that branch, 

 or what corresponds to the stem ; and every part around it, 

 including the disk, mtist be of a phyllous nature, that is, a sub- 

 division of the stem, taking this as the main midrib of the whole 

 plant. 



The whole flower is a cladophyl or branch, and all its parts 

 correspond to lobes or teeth of that cladophyl. 



* This term is unfortunately also used for the central florets of a 

 composite flower. 



