DOUBLE FLOWERS. 39 



5. An Amentaceous aggregate flower has a filiform, thread- 

 shaped receptacle, along which are disposed amentaceous squama, 

 scales that form an amentum, or catkin, as in Xanthium, Ambro- 

 sia, Parthenium, Iva, Alnus, Betula, Salix, Populus, Cory- 

 lus, Carpinus, Juglans, Fagus, Quercus, Liquidambar, Cyno- 

 morion, Ficus, Dorstenia, Parietaria, Urtica, Pin us, Abies, 

 Cupressus, Thuya, Juniperus, Taxus, and Ephedra. 



6. A glumose aggregate flower has a filiform receptacle, the 

 base of which is furnished with a common glume, husk, as in Bro- 

 mus, Festuca, Avena, Arundo, Briza, Poa, Aira, Uniola, Cy- 

 nosurus, Melica, Elymus, Lolium, Triticum, Secale, Horde- 

 um, Scirpus, Cyperus, and Carex. 



7. A spadiceous aggregate flower is, when there is a recepta- 

 cle common to many florets, placed within a spatha or sheath ; 

 such a receptacle is called a spadix, and is either branched, as in 

 palms, or simple. In this last case the florets may be disposed 

 either all round it, as in Calla, Dracontium, and Pothos;... 

 on the lower part of it, as in Arum ;...or on one side of it, as in 

 Zostera. 



CHAP. XX. 



OF LUXURIANT FLOWERS, COMMONLY CALLED 

 DOUBLE. 



A FLOWER is said to be luxuriant, when some of the parts 

 of fructification are augmented in number, and others thereby 

 excluded. The luxuriancy is commonly owing to the luxurian- 

 cy of its nourishment ; the part multiplied is usually the corolla, 

 but sometimes the calyx also; and by this increase of the covers, 



