8TRUGTURAL BOTANT. 91 



2. Clusters with Sessile Flowees. 



174. A spike is that form of flower-cluster in whicli 

 tlie flowers, all sessile, or nearly so, are arranged along a 

 common axis of inflorescence. It differs from a raceme 

 by having its flowers not pedicelled. (PI. II., 15.) 



The flowers are spiked in a great many plants. The 

 so-called spikes of Grasses are compound spikes, bearing 

 little spikes, or spikelets, instead of, single or simple flow- 

 era (the spikelets of this order compose also racemes and 

 panicles). 



A spikelef, in grasses, is an axis, or a rhaohis, subtended 

 by a pair of scales, which we call glumes (the latter rarely 

 solitary, or altogether wanting), and supporting one or 

 more naked flowprs, either perfect or imperfect,* the one 

 flower or each of the several flowers, as the case may be, 

 between another pair of scales, called pales (rarely em- 

 braced by a solitary pale). In descriptive botany, a pair 

 of pales, and even a single pale, are usually called flowers, 

 whether with or without essential organs. The scales are 

 distichously arranged, ((brasses have commonly 3 sta- 

 mens, rarely 1, 2, or 6, and a simple ovary, with 1 ascend- 

 ing ovule, 2 styles, and 2 feathery stigmas.) 



A spadix is a fleshy spike enveloped by a large leaf- 

 like bract, which is called a spai/ie, as in Indian Turnip, 

 Skunk-Cabbage, Calla, etc. (PI. U., 25.) 



A catkm or ament is a slender, often pendulous spike, 

 with scaly, deciduous bracts beneath the sessile flowers. 

 This sort of inflorescence is seen in Oak, Beech, Birch, 

 Willow, etc. (PI. II., 21.) 



A head is a round or roundish duster of sessile flow- 

 ers, or a short spike. This sort of inflorescence belongs 

 to the Button-bush, Eed Clover, etc. (PI. II., 24 ; YII., 2.) 

 The head may be surrounded by empty bracts, forming 

 an involucre, as in Composites. (PI. VII., 7.) 



