Page:An introduction to physiological and systematical botany (1st edition).djvu/139

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species of Trifolium, either annuals, as glomeratum, t. 1063, or perennials, as fragiferum, t. 1050.—The knobs in these instances are only of annual duration; in the Paeonia, Paeony, t. 1513, and Spiræa Filipendula, Dropwort, t. 284, they are perennial.—In the Orchideæ of Europe they are mostly biennial. The root in many of the latter consists either of a pair of globular or oval bodies, as in Satyrium hircinum, Engl. Bot. t. 34, Ophrys aranifera, t. 65, and apifera, t. 383; or are palmate, that is, shaped somewhat like the human hand, as in Orchis maculata, t. 632. Of these globular or palmate knobs or bulbs one produces the herb and flowers of the present year, withering away towards autumn, and the other is reserved for the following season, while in the mean time a third is produced to succeed the latter. The knobs of Ophrys spiralis, t. 541, are formed three or four years before they flower, and their flowering appears to be occasionally deferred to a more distant period. The root of Satyrium albidum, t. 505, consists