May, 1912. 



K\0\VLi:nGE. 



187 



vegetative organs and flowers, periodic phenomena, vegetative 

 reproduction, germination, and other aspects of marsh vege- 

 tation, inchiding much that is new. One of the most remarkable 

 plants which he describes is an aquatic dodder, Ciisciita alba, 

 which grows as a submerged parasite on \arious water-plants 

 in Sardinia and Algeria. 



VKGETATION OF CAITHNESS.— In The Vegetation 

 itf Caithness considered in relation to the Geology, C. B. 

 Crampton has published, under the auspices of the Committee 

 tor Hritisli \'egetation. a most important and interesting study 

 of vegetation as developed under the influence of geological 

 and physiographical factors. In the Preface, Dr. \V. G. Smith, 

 who has done so much pioneer work in botanical surve> — 

 along with his brother, the late Robert Suiitli, he laid the 

 foundations of systematic field-work and mapping of vegetation 

 in Hritain — points out that this memoir on Caithness proceeds 

 beyond a mere description of the vegetation. While this 

 descriptive work has been the main theme in the successive 

 memoirs published by K. and W. G. Smith, Smith and Rankin, 

 Moss, Lewis, and others, " there has been an increasing 

 tendency to consider other aspects of the ecological grouping 

 of plants. In each area dealt with, new plant-communities 

 have been discovered and compared with other known types, 

 both as regards floristic composition and ecological characters. 

 It has been more and more realised that some ecological 

 groups are of a higher order than others, and so have arisen 

 the concepts of a greater unit, the plant formation, and lesser 

 units — subformations, associations, societies, and so on. The 

 relation exibting between plants associated together in plant- 

 comnnmities. and the habitats occupied by each vegetation 

 unit, has received greater consideration in each successive 

 memoir." 



.-\s Hr. Smith points out. this Caithness memoir is the first 

 attempt by a member of the (leological Survey to deal with 

 the vegetation of an area on which he has worked, and this is 

 especially welcome since in former botanical surveys sufficient 

 attention has not been paid to the geological considerations 

 bearing on the topography or physiography of the district 

 dealt with. The chief theme underlying this memoir is the 

 distinction of stable from unstable formations, and such 

 topics as the influence of physiographic factors on the 

 historical development of the vegetation, and the effect of 

 glaciation on plant distribution, are discussed in a way not 

 hitherto attempted. 



The author discusses in detail the conditions determining 

 the formation of peat since early post-glacial times, and the 

 changes in the vegetation of the peat leading on to the present 

 period of retrogression — about two-thirds of Caithness are 

 now covered by peat, which was formerly much more exten- 

 sive. The accumulation of peat has been favoured by (1) the 

 plateau-like topography and its influence on the prevalent 

 winds, rainfall, and drainage; (21 the condition of the surface 

 of the land at the retreat of the ice-sheet, when the surface 

 was either bare rock or drift, the soil-bacteria that promote 

 nitrification were banished and returned slowly owing to the 

 cold ,ind the accumulation of acid humus, and stagnant 

 conditions alternated with hard unweathered surfaces of rock 

 or boulder-clay ; (3) the latitude of Caithness and its geo- 

 graphical position relative to the edge of the continental shelf. 



The subscijuent history of the vegetation is indicated by 

 plant-remains in the peat. "At first the plant associations 

 were probably of a tundra-like nature, shallow-rooted, creep- 

 ing, or cushion-like, and periodically frozen or soaked in 

 ice-cold water. As the cold grew less, and more humus 

 accumulated, a bog flora established itself in the hollows, but 

 over wide areas a dwarf scrub of birch seems to have obtained 

 a footing." Later came a forest period with pines, which 

 subse(|uently disappeared, their advent and decline being 

 attributable probably to climatic changes. In recent times 

 the occurrence of extensive areas of peaty moorland has acted 

 as a barrier on the landward side to all plants incapable of 

 competing with moorland associations, hence plant-migration 

 has taken place mainly along the coast and river systems, and 

 by the aid of man. 



The author proposes that dominant plant formations which 

 occupy ground comparatively stable from the geological stand- 

 point should be termed stable or palacogeic formations, since 

 the ground they cover mainly owes its features to past 

 geological processes ; while for the limiting and dissecting 

 formations, often found in all stages of progressive association 

 and succession, from the migratory nature of the geological 

 agents of erosion and deposition, he suggests the terms 

 migratory or neogeic formations, since the ground they occupy 

 owes its features to recent geological processes. In the case 

 of Caithness, this method resolves the vegetation into one 

 dominant stable formation, the moorland, and several 

 migratory formations in the belts along the coast, the 

 ramifications of the drainage system, and the alpine centres. 

 These various formations are then dealt with in detail, with 

 numerous examples of associations in representative localities. 



The author links up his classification with that of Cowles, 

 who has defined three types of cycles of vegetative succession 

 — (1) regional successions, due to secular change, the most 

 important in Britain being the post-glacial invasion of soul hern 

 forms into northern regions, accompanying and following the 

 retreat of the ice; (2) topographic successions, of much 

 greater rapidity and associated with topographical changes 

 resulting from the activities of such agents as running water, 

 wind, ice, gravity, and leading in general to erosion and 

 deposition, the influence of erosion being generally destructive 

 to vegetation or at any rate retrogressive (tending to cause 

 departure from the mcsophytic typel while that of deposition 

 is constructive or progressive (tending to cause an approach 

 towards the mesophytic type) ; and (3) biotic successions, due 

 to plant and animal agencies. The regional successions are 

 exemplified in Caithness in successions of plant remains, 

 tundra, forest, and moorland, in the peat-mosses, such as were 

 first demonstrated in Dentnark by Steenstrup and recently in 

 Britain by Lewis ; the plant formations effecting these 

 regional successions correspond to Crampton's stable or 

 neogeic formations. The topographical successions (normally 

 limited to the coastal belt, river systems, and alpine centres) 

 and the biotic successions are included in Crampton's 

 migratory or neogeic formations. 



Altogether, this memoir may be said to break a good deal of 

 entirely new ground as regards descriptive ecology in Britain. 

 A notable feature in the author's thorough and instructive 

 treatment of the vegetation of his area is the inclusion of the 

 more abundant and characteristic mosses, liverworts, and 

 lichens in his floristic lists, and his demonstration of the impor- 

 tant part played by these plants in the various associations. 

 The importance of the peat-mosses (Sphagnaceae) has, of 

 course, long been realised, but comparatively little attention 

 has been paid by previous writers on descriptive ecology to 

 other mosses which, along with lichens and lu;patics, enter 

 largely into the composition of various plant-societies and 

 in places form a striking and conspicuous element in the 

 vegetation. For instance, Crampton distinguishes a Rhacomi- 

 trium bog association, in which the woolly fringe-moss (7?. 

 laniiginosnin) is dominant over considerable areas. It is 

 characteristic of the author's thoroughness that he has not 

 been content with " Sphagnum spp.," but has had his 

 sphagnums named, as well as the lichens and liverworts. In 

 connexion with the latter group, mention may be made of 

 Macvicar's recent work on the distribution of the liverworts of 

 Scotland. 



IRON BACTERIA. — Our knowledge of these remarkable 

 organisms, largely due to the work of Winogradsky and of 

 Molisch (see "Knowledge," March. IQH, page 105), has 

 recently been supplemented by Lieske ijahrh.fiir iciss. Hot., 

 1911). This writer has studied Spirophylhnn fernigiiieuin, 

 which, unlike Leptothrix studied by Molisch, does not grow in a 

 medium containing organic matter, nor in an iron-free medium, 

 nor in a medium containing iron salts other than ferrous 

 carbonate or bicarbonate, nor salts of any of the other metals. 

 Lieske's most important result, however, is his experimental 

 proof that this bacterium can utilise the carbon of carbon 

 dioxide in the total absence of any other source of carbon. 

 The nutrient medium contained inorganic salts in solution. 



