Whilst remaining essentially the organ of photosynthesis and transpiration, the leaf takes on other functions in some species. The most notable of these is the climbing function. Tendrils are slender extensions of the leaf, and are of three types. In Clematis spp, the leaf petiole curls round the stems of other plants or garden structures in order to support the climber (see Figure 5.6(d)). In sweet pea (Lathyrus odoratus), the plant holds on with tendrils modified from the end-leaflets of the compound leaf. In the monocotyledonous climber, Smilax china, the support is provided by modified stipules (found at the base of the petiole). In cleavers (Galium aparine), both the leaf and stipules, borne in a whorl, have prickles that allow the weed to sprawl over other plant species.
Buds and bulbs are composed mainly of leaf tissue. In the former, the leaves (called scales) are reduced in size, hard, and brown rather than green. They tightly overlap each other, giving protection to the delicate meristematic tissues inside the bud. In a bulb, the succulent, light-coloured scale leaves contain all the nutrients and moisture necessary for the bulb's emergence. The scales are packed densely together around the terminal bud, minimizing the risk that might be caused by extremes of climate, or by pests such as eelworms or mice. In the houseplant Bryophyllum daigremontianum, the succulent leaf bears adventitious buds that are able to develop into young plantlets.
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