. Foundations of botany. Frequently the lower pedicels of a cluster on thegeneral plan of the raceme are longer than the upperones and make a some-what flat-topped cluster,like that of the hawthorn,the sheep laurel, or thetrumpet creeper. Thisis called a corymb. In many cases, for ex-ample the parsnip, theSweet Cicely, the gin-seng, and the cherry, agroup of pedicels of —catkins of wniow. nearly equal length ^i, stamlnate flowers ; ^, plstUlate 1 It is hardly necessary to say that the teacher will find it better in everyway, if material is abundant, to begin the study of flowe
. Foundations of botany. Frequently the lower pedicels of a cluster on thegeneral plan of the raceme are longer than the upperones and make a some-what flat-topped cluster,like that of the hawthorn,the sheep laurel, or thetrumpet creeper. Thisis called a corymb. In many cases, for ex-ample the parsnip, theSweet Cicely, the gin-seng, and the cherry, agroup of pedicels of —catkins of wniow. nearly equal length ^i, stamlnate flowers ; ^, plstUlate 1 It is hardly necessary to say that the teacher will find it better in everyway, if material is abundant, to begin the study of flower-clusters with theexamination of typical specimens by the class. 188 FOUNDATIONS OF BOTANY ,4% spring from about the same point. This produces aflower-cluster called the umbel (Fig. 130). 199. Sessile Flowers and Flower-Clusters. — Often thepedicels are wanting, or the flowers are sessile, and thena modification of the raceme is produced which is calleda spike^ like that of the plantain (Fig. 132). Thewillow, alder, birch, poplar, and many other commontrees bear a short, flexible, rather scaly spike (), which is called a catkin. The peduncle of a spike is often so much short-ened as to bring the flowers into a somewhat globu-lar mass. This is called a head (Fig. 132). Around the base of the head usuallyoccurs a circle of bracts knownas the involucre. The samename is given to a set of bractswhich often surround the basesof the pedicels in an um
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