4 THE STRUCTURE OF FLOWERS. 



constitute tlie Anclroecium. Lastly, there are represented 

 two * whorls of Carpels forming the Gynoeciura f or Pistil. 

 The outermost whorl of carpels is superposed to the sepals, 

 the innermost to the petals. 



There may be additional structures in flowers, such as 

 disks, honey-glands, etc. ; but as these, when they occur on 

 the floral-receptacle, are merely cellular protuberances and 

 form no part of the floral whorls proper — not being foliar in 

 their origin— they may be omitted, especially as their posi- 

 tion is by no means constantly the same in all flowers.J 



The Principles of Vakiation. — Having thus assumed an 

 ideal type, we may at once consider the " Principles of 

 Variation," as I propose to call them, in accordance with 

 which the different members of flowers can be altered; so 

 that by means of various combinations of these principles all 

 the flowers in the Vegetable Kingdom can be brought under 

 this one fundamental plan. 



There are five principles which require special considera- 

 tion. They are usually designated by the terms Number, 

 Arrangement, Cohesion, Adhesion, and Form. 



"Number" refers to the number of whorls and the 

 number of pai-ts in each whorl. If two or more whorls 

 contain the same number of parts or be multiples of one 

 another, they are said to be " symmetrical " or " isomerous." 

 If they differ in the number of parts they are " unsym- 

 meti-ical " or " anisomerous." 



"Arrangement" refers to the relative positions of the 



* Why I assume two whorls for the pistil, instead of one only, as is 

 generally done, will be understood hereafter. I have since found that 

 Robert Brown carae to the same conclusion (Col. WorJcs, i. 293). 



t I adopt the spelling ayncecium for the sake of uniformity ; it may 

 be regarded as a shortened form of Gyncecoecium. 



J I do not here allude to certain glandular structures, which may 

 be the homologucs of arrested organs. 



