196 



KNOWLEDGE. 



[September, 1908. 



leaves, and sending up fleshy scaly stems which bear a 

 number of droopincr flowers of the same hue. The Yellow 

 Bird's-nest (as it is called, from its resembUmce to the 

 Bird's-uest Orchis) is a rare and rather southern plant 

 in Britain, growing in thick woods, generally under Beech 

 or Fir trees. Its whole appearance — the al^sence of leaves 

 and of green colouring matter — suggest a parasitic or 

 saprophytic habit. If we examine its curiously tangled 

 root system, it ^"ill he found to be intimately associated 

 with the mycelium, or webby underground portion, of a 

 fungus ; and the plant is always found in a soil rich in 

 humus — in the leaf-mould that forms under thick trees. 

 The plant feeds on the decaying vegetable matter, and 

 apparently the j)rocess is rendered easier — or, perhaps, 

 possible — by the presence of the fungus, whose thready 

 stems are closely interwoven with the tissue of the root. 

 The relations existing between the fungus and the 

 Monofropa, with reference to the process of assimilation, 

 however, have not yet been made clear. 



The Gentian family is tolerably closely related to that of 

 the Heaths, but it was association, rather than affinity, 

 that suggested the bracketing of the two in the present 

 sketch. Like the Heaths, this is one of those groups of 

 plants whose presence makes one glad with the thought 

 that towns are left far Ijehind, and that sand-dune, moor, 

 and mountain are around one. And while they differ 

 from the Heaths in being all herbaceous, they rank worthily 

 with them in attractiveness of form and colour. The two 

 leading genera are Gentiana and Erythnea. The British 

 Gentians have all blue or purplish flowers, the Centaurys 

 all pink. Our native Gentians are five in number. The 

 largest is G. Pneumonanthe, the so-called Calathian Violet, 

 a plant confined to England, so far as the British Islands 

 are concerned. Its stems are about a foot high, ending in 

 large upright deep blue bells with five segments, each 

 bearing a pale stripe. Next come our two commonest 

 species, G. AmareUa and G. campestris, small upright 

 annuals, growing on dry heaths and pastui-es. In habit 

 and leaf these two resemble each other, but they may lie 

 easily distinguished by the calyx, which has five equal 

 segments in G. AmareUa, four unequal segments in G. 

 campestris. The corolla is likewise five-parted in the 

 former, four-parted in the latter. Finally we have two 

 small mountain species. G. 

 nivalis is a tiny annual, with an 

 upright stem and bright blue 

 flower, found only on high 

 mountains in Perth and I'orfar. 

 Lastly we have G. veriia, the 

 most beautiful of our Gentians. 

 It is a little tufted perennial, 

 which in spring sends up a 

 profusion of almost stemless 

 flowers of the most wonderful 

 vivid blue colour. It is a 

 plant of limestone rocks, in 

 England confined to sub-alpine situations in the north, 

 in Ireland occupying a large area of low-lying as 

 well as upland limestone country chiefly around Giilway 

 Bay. Though so local, it is usually abundant where 

 it occurs ; and the Galway pastures in April, all 

 painted with its blossoms, form a sight never to be 

 forgotten. 



The Centaurys recall, in their dwarf upright groivth and 

 opposite pairs of leaves, the annual Gentians ; but their 

 bright pink flowers render them easily recognizable among 

 all the summer vegetation. Several forms occur, to which 

 some botanists assign specific rank, while others treat them 

 as sub-species of our aggregate, E. Centaureum. It is 

 needless to enter into the charactei-s of these forms in this 



campestris. Natural size. 



place. Allied to Erythrxa is Cicendia, of which our only 

 species, C. filiformis, is a very slender and almost insignifi- 

 cant ujmght annual like a tiny Centaury with four-parted 

 yellow flowers. It grows on damp sandy ground in the 

 south-west of England and of Ireland. The genus Cklora 

 has likewise only one British species, the well-known 

 Perfoliate Yellow-wort, C. perfolinta, an annual plant easily 

 recognized by its upright almost unbranched stems, with 

 opposite glaucous leaves joined at their base, and bright 

 yellow flowers. The perfoliate character 

 of the leaves is worth noting, as this is 

 one of the few British plants displaying 

 that feature. 



The two remaining British Gentianaceie 

 are plants differing widely from any which 

 we have considered ; a difference to be 

 chiefly accounted for, no doubt, as in the 

 case of Motiotropa, by the different walk 

 of life which they have chosen. One is 

 a marsh plant, the other a water jilant. 

 The Bog-bean {Menijanthes trifoliata) 

 grows in wet bogs and on the edges of 

 pools. It is fleshy in all its parts, 

 thick as one's finger, often creep for several yards. They 

 bear leaves with three broad egg-shaped leaflets, and 

 racemes of remarkably pretty flowers. These are pink 

 or white, and the inner side of the petals is densely 

 covered with curious thick white hairs, which give the 

 flowers a most peculiar appearance, differing from that of 

 any other British plant. The last plant of the Gentian 

 family is Limnanthemnm peltatum, a thorough aquatic, 

 living in ponds and slow rivers. This plant has adopted 

 the floating leaves which the Water-Lilies and other 

 plants find serviceable, and it looks very like a miniature 

 Water-Lily, with its round leaves and yellow blossoms 

 rising from among them. The root-stock is far below, 

 creeping in the mud, and sends up at intervals to the 

 surface shoots bearing the foliage and flowers. This is 

 rather rare as a British plant — at least as a native — 

 occurring chiefly in the midland coimties of England. 



Fig. 6.— Per- 

 foliat« leaves of 

 the Yellow-wort. 

 Half natural size. 



The stems, as 



MODERN COSMOGONIES. 



By Agnes M. Cleeke. 



IV.— TIDAL FEICTION AS AN AGENT IN 

 COSMOGONY. 



The effects of tidal friction are of almost infinite com- 

 plexity. How it ^yil\ act in each particular case cannot be 

 predicted off-hand ; it is a matter for detailed enquiry. 

 Mutually countervailing influences have to be taken into 

 account ; nor is the balance easy to strike. How it 

 inclines may indeed often depend upon qualities and 

 relations of the bodies concerned which lie outside the 

 range of what can be distinctly ascertained. All that can 

 be hoped for, then, is to arrive at estimates neither 

 misleading by their ostensible precision, nor yet so 

 vague as to be wholly uninstructive, of the part played 

 by tidal forces in moulding the history of connected 

 globes. 



The assumption that they attract one another as if the 

 mass of each were collected at its centre, is one of those 

 convenient fictions without which the advancing feet of 

 science would be impeded by entangled thickets of 

 illusory refinements and superfluous elaborations. Tlie 

 fiction would correspond with fact only if the globes were 

 truly spherical, and they could be truly spherical only if 



