Spiraea Ulmaria, L., and its Bearing on the Problem of Xeromorphy in Marsh Plants

Abstract

I n the first, which belongs to the Q Uhwrta, are Spiraea Ulmat-ia, L., S. pdnzata, Thunb., and S. vestita, Wall. These are closely allied Old Cf. Yapp ('08, two papers), Cog), and ('10). e. g. S3irat-n UInmria. e.g. Phragmilu romnrunis, Vibuntum Opulrcs, S a l i x spp., Bc. ' In the sense nxd by Linnaeus, Bentham nnd Hooker, m d others, 6. Wenrig ('88). Other authors, probnbly rightly, separate the several sections of Spirara as distinct genera, e.g. Focke ('94).

Studies in the Morphogenesis of Leaves

“…Data of Zalenski (1904), Rippel (1919) and others support the view that stomatal frequencies do not rise indefinitely with level of insertion on the shoot. Yapp (1912) recorded several observations which are inconsistent with the current hypothesis. He found, for instance, that in successive leaves of a non-flowering shoot of Spiraea Ulmaria there was not a gradient of increasing stomatal frequency from leaf to leaf, but an increase to a maximum in the summer, followed by a decrease in autumn.…”

The evolution and functional significance of leaf shape in the angiosperms

“…The result of how this phenomenon might affect a leaf has long been observed: regions of leaves lying furthest from the main supply channels are the first to 'wither' when exposed to strong winds ( Fig. 4; Yapp 1912). Leaf lobing represents an effective removal of this potentially stress-prone tissue and has been suggested as an adaptation to dry conditions (Thoday 1931;Givnish 1979).…”

Ecological Variations in the Leaf Anatomy of Selected Species of Cercocarpus

“…There are no hairs in the vegetative bud of Spiraea ulmaria ( Tourn. ) Hill., but pubescence develops and increases as buds unfold, appearing first along the larger veins of the young leaves ( Yapp, 1912 ). Shields ( 1950 ) also states that living trichomes do not protect the plant from excessive transpiration as do dead trichornes which form protective layers.…”

“…8d), and C. intricatus. Mesophyll.-A higher ratio of palisade to spongy chlorenchyma layers has been considered, in dicotyledons, to b e a xeromorphic feature ( e.g., Yapp, 1912;Shields, 1950;Fahn, 1964;Esau, 1965 ). An early investigator, Dufour ( 1887) , and more recently Wylie ( 1951 ), as well as numerous oth ers have come to the conclusion that differences in palisade development in sun and shade leaves are exclusively a response to differences in light intensity.…”