. The Botanical Class-Book and Flora of Pennsylvania. loping inthe one way. Thus the heads of all the Composite© are cen-tripetal, the flowers expanding regularly from the margin orcircumference to the centre; while the branches that bear theheads are developed in the centrifugal mode, the terminal orcentral heads first coming into flower. Tiiis is exactly rever-sed in all the Labiatse (plants of the mint tribe^where thestem developes in the centripetal mode, and the axillary clus-ters of the flowers being produced in the form of a generalraceme or spike, which blossoms from below upwards; whi
. The Botanical Class-Book and Flora of Pennsylvania. loping inthe one way. Thus the heads of all the Composite© are cen-tripetal, the flowers expanding regularly from the margin orcircumference to the centre; while the branches that bear theheads are developed in the centrifugal mode, the terminal orcentral heads first coming into flower. Tiiis is exactly rever-sed in all the Labiatse (plants of the mint tribe^where thestem developes in the centripetal mode, and the axillary clus-ters of the flowers being produced in the form of a generalraceme or spike, which blossoms from below upwards; whilethe flowers from each cluster form a cyme, and expand in thecentrifugal manner.— Gray. 162. The following are the principal varieties of centri-petal inflorescence—the spike, raceme, corymb, umbel, head,spadix, ament, panicle, and thyrse. 163. Spike (Fig. 75,) is an inflorescence, where the ses-sile Sowers in the axils of the bracts are arranged aloug an INFLORESCENCE. 55 elongated commom peduncle, as in the Plantain, Verroin,Mullein. 75. 164. The Raceme (Fig. 70,) is the same as the epike,except that the flowers are raised on pedicels; as in the WildCherry, Hyacinth, Pyrola. 165. The Corymb (Fig. 77,) is the same as the rasemo?with the lower pedicels elongated, so as to elevate all theflowers to nearly or quite the same level, as in the Hawthorn,Crab-Apple. 77. 78.
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