Floristik, Geographie, Systematik etc. 153 



Acacia frora Western Australia. (Scott, bot. Review L. 2. 

 p. 96—99. 1912.) 



Floristic descriptions of the following: A. densiflora n. sp., A, 

 longispinea n. sp., A. nncineUa Benth. (fruit characters), A. Ariquetra 

 Benth. (distinction from A. Metsstiert Lehm.), A. pyrifolia DC. n. var. 

 (distinction of" a tree-form on the piain from a shrub near river), 

 A. microbotrya Benth. (fruit), A. Lindleyi Meissn. (distinction from 

 A. subcoerulea Lindl.), A. dictyophleba F. v. INI. (fruit), A. aciphylla 

 Benth. (fruit), A. ephedroides Benth. (fruit), A. stereophylla Meissn. 



W. G. Smith. 



Oliver, F. W., The Shingle Beach as a Plant Habita t. 

 (New Phytologist XI. 3. p. 73—99. 1 plate. 8 figs. 1912.) 



Shingle Banks arise when waste stony materials are so influen- 

 ced by little currents that they are raised to form banks or beaches; 

 as a plant habitat they have not been described in Britain, although 

 such beaches extend to 300 miles in England and Wales. This 

 paper is a Condensed summary of the author's extensive observations. 



Four types are distinguished: 1) Fringing type, where shingle 

 forms a strip in contact with che land (e. g. S. W. of Dieppe); the 

 remaining types are produced when the current leaves the shore. 

 viz. — 2) Shingle spit produced when a coast-line bends sharply 

 landwards, while the shingle is carried by currents to form a bank 

 attached to the shore at its proximal end and terminates distally 

 as a hook directed landwards (e. g. Hurst Castle in Isle of 

 Wight and Blakeney in Norfolk; 3) Bar, when a shingle spit 

 after leaving the land returns so that there is a land-connection at 

 both ends; 4) Apposition type, when the current fails to transport 

 drift to the end of the bank, and deposition takes place on the flank, 

 hence parallel banks are formed (Dungeness). 



The formation of the Shingle Spit is illustrated by a series of 

 diagrams and is described in considerable detail (see original) with 

 reference to the relation of the shingle to the littoral shelf, the 

 formation of the terminal and lateral hooks on the land ward side, 

 curvature of spit, and the changes which occur between the spit 

 and the land, marsh-formation. A succession of phases is recognised 

 in the evolution of a spit: growth in lenght in youth , hook-formation 

 in maturity, and these are traced to the constructive and destructive 

 action of tidal flow. These phases also find expression in the suc- 

 cession of the Vegetation — pioneer plants giving place to those of the 

 spit's more stable phase. The mobility of shingle banks is discussed 

 under the heads of wave impact, percolation of water on the sea- 

 ward side and outflow on the landward side, and undercutting on 

 the lee side by tidal and other currents. The result of the action 

 of one or more of these processes is that the shingle spit tends to 

 move slowly shorewards as illustrated on Chesil Bank (Dorset). 

 When on the landward side of a bank there are several lateral 

 hooks, this shoreward movement leads to "hook-slide", the hooks 

 being "embedded as the main trunk of a thickening dicotyledonons 

 tree embeds its branches". This phase is demonstrated by the distri- 

 bution of Snaeda fruticosa which is marginal on the main bank and 

 hooks, and retains its position on the latter after they have become 

 embedded in the main bank. 



Various types of habitat are presented with respect to exposure, 

 mobility of the shingle, and in the soil collected amongst the coar- 



