STRUCTURAL BOTANY. 91 



2. Clusters with Sessile Flowees. 



1 74, A spike is that form of flower-cluster in which 

 the 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 compoimd spikes, bearing 

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

 ers (the spikelets of this order compose also racemes and 

 panicles). 



A spikelety in grasses, is an axis, or a rhachis, subtended 

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

 solitary, or altogether wanting), and supporting one or 

 more naked flowers, 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. (Grasses 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 spathe, as in Indian Turnip, 

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



A catkin 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. (tl. II., 21.) 



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

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

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

 The head may be suiTOunded by empty bracts, forming 

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



