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Morphology, Anatomy, and Distribution of Capitate Glandular Trichomes on Selected Trifolium Species

Dep. of Biology, Dalhousie Univ., Halifax, NS, Canada B3H 4J1

^* Corresponding author.

Glandular trichomes may impart insect resistance to crops. This study was conducted to determine the morphology, anatomy, and distribution of glandular trichomes on Trifolium pratense L., T. medium L., T. hybridum L., and T. repens L. Fluorescence microscopy, scanning electron microscopy, and transmission electron microscopy were used to facilitate this study. Procumbent and erect glandular trichomes were found on cultivars of these species. Both procumbent and erect glands arose from epidermal cells, were capitate, and had thick-wailed stalks. The heads of the procumbent glands were long and thin, consisting of four to eight layers of cells, each layer consisting of one to four cells. By contrast, the heads of the erect glands were globose and not organized in layers, although they were multicellular. Leaves, stems, peduncles, and sepal surfaces had procumbent and erect glands. All floral organs, other than sepals, were devoid of procumbent glands, except in alsike clover (T. hybridum L.) specimens, where these glands were found on the gynoecium. Tissue-culture grown white clover (T. repens L.) leaflets showed the greatest density of procumbent glands, these being located abaxially only. Erect glands frequently appeared on petioles and on foliar margins, near vein endings, and in association with simple (vegetative) hairs. On the basis of previous evidence, it is proposed that the two kinds of glandular trichomes present on these Trifolium species may be involved in plant defense.

Key Words: Procumbent trichomes • Erect trichomes • Trifolium pratense L. • T. repens L. • T. hybridum L. • T. medium L.

Received for publication September 21, 1987.