38 LETTER XXIX. 



Before we proceed further, let me detain you a 

 moment with the meaning of the word disk : a term 

 that has just occurred. We formerly had it as the 

 name of the central part of a compound or rather a 

 composite flower. (Vol. I. p. 203.), comprehending all 

 the florets which have a tubular structure with an 

 equally divided border ; in the present instance it is 

 used in a different sense. It means a supernume- 

 rary organ, different from the stamens or petals, 

 and originating at the base of one or other of them. 

 Nothing can well be more variable in its nature than 

 this disk ; in the Mignonette it is, as you see, a one- 

 sided, hairy lobe ; in some plants it is a fleshy ring 

 surrounding the ovary ; in others a small number of 

 glands in the same place ; in Black Horehound you 

 formerly saw it in the state of a green fleshy base to 

 the lobed ovary (Vol. I. Plate XVI. 1. fig. 4. a. and 

 6. a.) •■, and in the poppy-flowered Pseony you will 

 find it constituting a deep purple case, enveloping the 

 ovaries, and cut into irregular segments at its edge. 

 In all these instances the disk is considered to be in 

 reality either corolla, or stamens, in a disguised 

 state ; in the example before us, it is to be referred 

 to the corolla. 



The ovary of the Mignonette {fig- 6.) is an oblong, 

 three-cornered, three-horned, one-celled case, having 

 its horns terminated by the stigmas, and its ovules 

 arranged in triple rows upon three narrow placentae 

 (^fig. 7. a. a.), corresponding with the principal angles 

 of the ovary. If viewed with a magnifying glass, the 



