COMPOSITE FLOWERS. 205 



they are much stouter than their stalks, the stem 

 would, in such a case, have to be expanded much 

 more in order to receive them ; in fact it would 

 become a receptacle such as you find in a Daisy. 

 The receptacle of a composite flower is therefore an 

 expanded part of a stem. 



You may also look at its structure in another way. 

 Take a spike of Ribgrass, an exceedingly common 

 weed, about which I shall say something at the end 

 of this letter ; place it by the side of a flower-head of 

 French Marigold ; let the letter e in both cases re- 

 present the base of the inflorescence, and b the top 

 of the spike of Ribgrass (Plate XVII. 2. fig. 1.), 

 and the centre of the disk of the French Marigold 

 (Plate XVII. 1. fig. 1.). Suppose the spike of Rib- 

 grass to be very much shortened, the number of 

 flowers upon it remaining the same ; the distance 

 from 5 to e will be proportionably diminished, and the 

 flowers will be much more crowded. Let this shorten- 

 ing be carried still further, the number of flowers 

 still remaining the same, and it is obvious that in 

 order to make room for the flowers, side by side, the 

 stem must expand horizontally; a receptacle will 

 then be produced, and a little reflection will shew you 

 that the letter b will then indicate precisely the same 

 parts in both plants : the centre of the French Mari- 

 gold being the same as the point of the spike of Rib- 

 grass. The receptacle of a compound flower is there- 

 fore both a contracted and expanded stem. 



With regard to the involucre, Rousseau has well ob- 

 served, that it has generally the property of opening 



