XX11 INTRODUCTION. 



alternate, etc. (32, 33), but very often their arrangement is different from that 

 of the leafy branches of the same plant. 



72. Inflorescence is 



centrifugal, when the terminal flower opens first, and those on the lateral 

 branches are successively developed. 



centripetal, when the lowest flowers open first, and the main stem con- 

 tinues to elongate, developing fresh flowers. 



73. Determinate inflorescence is usually centrifugal. In determinate in florescence 

 is always centripetal. Both inflorescences may be combined on one plant, for 

 it often happens that the main branches of an inflorescence are centripetal, 

 whilst the flowers on the lateral branches are centrifugal : or vice versa 



74. An Inflorescence is 



a Spike, or spicate, when the flowers are sessile along a simple undivided 

 axis or rhachis. 



a Raceme, or racemose, when the flowers are borne on pedicels along a 

 single undivided axis or rhachis. 



a Panicle, or paniculate, when the axis is divided into branches bearing 

 two or more flowers. 



a Head, or capitate, when several sessile or nearly sessile flowers are col- 

 lected into a compact head-like cluster. The short, flat, convex or conical axis 

 on which the flowers are seated, is called the receptacle, a term also used for 

 the torus of a single flower (135). The very compact flower-heads of Composites. 

 are often termed compound flowers. 



an Umbel, or umbellate, when several branches or pedicels appear to start 

 from the same point and are nearly of the same length. It differs from the 

 head, like the raceme from the spike, in that the flowers are not sessile. An 

 umbel is said to be simple, when each of its branches or rays bears a single 

 flower ; compound, when each ray bears a partial umbel or umbellule. 



a Corymb, or corymbose, when the branches and pedicels, although starting 

 from different points, all attain the same level, the lower ones being much 

 longer than the upper. It is a flat-topped or fastigiate panicle. 



a Cyme, or cymose, when branched and centrifugal. It is a centrifugal 

 panicle, and is often corymbose. The central flower opens first. The lateral 

 branches successively developed are usually forked or opposite (dichotomous 

 or trichotomous), but sometimes after the first forking the branches are no 

 longer divided, but produce a succession of pedicels on their upper side forming 

 apparently unilateral centripetal racemes ; whereas if attentively examined, it 

 will be found that each pedicel is at first terminal, but becomes lateral by the 

 development of one outer branch only, immediately under the pedicel. Such 

 branches, when in bud, are generally rolled back at the top, like the tail of a 

 scorpion, and are thence called scorpioid. 



a Thyrsus, or thyrsoid, when cymes, usually opposite, are arranged in a 

 narrow pyramidal panicle. 



75. There are numerous cases where inflorescences are intermediate between 

 some two of the above, and are called by different botanists by one or the other 

 name, according as they are guided by apparent or by theoretical similarity. 

 A spike-like panicle, where the axis is divided into very short branches form- 

 ing a cylindrical compact inflorescence, is called sometimes a spike, sometimes a 

 panicle. If the flowers are in distinct clusters along a simple axis, the inflores- 

 cence is described as an interrupted spike or raceme, according as the flowers 

 are nearly sessile or distinctly pedicellate ; although when closely examined the 

 flowers will be found to be inserted not on the main axis, but on a very short 

 branch, thus, strictly speaking, constituting a panicle. 



76. The catkins (amenta) of Ameyitacea, the spadices of several Monocoty- 

 ledons, the ears and spikelets of Grasses are forms of the spike. 



77. Bracts are generally placed singly under each branch of the inflores- 



