78 



MORPHOLOGY, OE COMPARATIVE ANATOMY. 



Fig. 136. 



Forms of Indefinite Inflorescence. Of the Indefinite Inflores- 

 cence the following are the most important forms : the spike, the 

 raceme, the corymb, the umbel, and the capitulum. 



Spike. The spike is a long simple axis or rachis bearing sessile 

 flowers, either standing at intervals, as in the Vervain (fig. 132), 

 or crowded, as in the common Plantain and many Sedges. 



Several modifications of the spike have distinct names. When 

 the rachis hears large, persistent, imbricated bract-scales, it forms 

 a cone or strobile, as in the Firs and Pines. When it is thick and 

 fleshy, with the flowers more or less imbedded in it, the 

 term spadix is applied, of which the Araceae furnish examples 

 (fig. 133) j the same term is con- 

 veniently retained when this fleshy axis is 

 branched, as in the Palms (fig. 134). The 

 so-called spikes of many Grasses, such as 

 Wheat, Barley, Rye-grass (fig. 135), Cat's- 

 tail-g'rass, c., are also compound spikes, 

 since in place of single flowers the rachis 

 bears spikelets or short axes with several 

 sessile flowers. The term catkin (amentum) 

 is applied to the pendent, often caducous, 

 spike-like inflorescence of the Willow, 

 Poplar, Birch (fig. 136), and the male in- 

 florescence of the Oak, Filbert, Chestnut, 

 &c. j in these the bracts have sometimes 

 one, sometimes several flowers in their 

 axils. The flowers in catkins are usually 

 unisexual. 



Male and female catkins 

 of the Birch. 



Raceme. The raceme differs from the spike in having the 

 flowers distinctly stalked, the main rachis being unbranched, as 

 in the Hyacinth, &c. 



Corymb. The corymb is formed when the flowers originate as in the 

 raceme, but the lower ones are raised on longer stalks than the upper 

 ones, so as to bring them all nearly on a level, as in Ornithogalum 

 (fig. 137), &c. 



As already noticed, a corymbose inflorescence sometimes grows out 

 into a raceme while the fruits are ripening, as is seen in many Crucifene. 

 The relation between the two forms, or, more properly, between the 

 panicled and the corymbose state of the same inflorescence, is well seen 

 in comparing a Cauliflower as fit for the table with the expanded in- 

 florescence of the same plant when allowed to run to seed. 



Panicle. A panicle is formed when the main rachis is more or 

 less branched ; it is hence a series of racemes on -a branched rachis. 

 The term panicled is often used in a general sense, to signify a 

 much-branched inflorescence, whether definite or indefinite. 



