1908.] 



KNOWLEDGE 



17 



most convenient of them all. There is in Scotland a cele- 

 brated seat inviting wayfarers to " rest and be thankful." 

 In its high and exposed situation this is sometimes 

 surrounded by a guard of Highland cattle, which by their 

 sturdy attitude seem planted on purpose to discourage 

 indolence. In our pursuit of the Pycnogonida, readers 

 may well think that by this time we must certainly have 

 reached a point if not for gratitude at least for justifiable 

 lassitude. But a final call is to be made on their en- 

 durance. The subject itself is in a stage more suggestive 

 of energetic advance than of somnolent repose. In the 

 concluding chapter, therefore, some notes will be offered 

 as to the opportunities which our own country clearly offers 

 for its investigation, and on the literature which is essential 

 for any one anxious to carry forward research instead of 

 re-diseovering what is already known. 



FAMILIAR BRITISH WILD FLOWERS AND 

 THEIR ALLIES. 



By R. Lloyd Praeger, b.a. 

 I.— THE PEA FAMILY.* 



The Order Leguminosee is one of the great plant-groups 

 of the world, myriad in number, ubiquitous in distribu- 

 tion, embracing every kind of plant from tiny herljs to 

 gigantic forest trees, and abounding in useful and hurtful 

 products and properties. As food-producing plants, it is 

 the seeds that are chiefly used. These, enclosed in the 

 pod that is so characteristic of this Order, and each con- 

 taining a good store of food-material for the use of the 

 young plant, are familiar to us as peas, beans, lentils, and 

 haricots. As fodder for domestic animals, the whole plant 

 is vahiable in the case of the Clovers, Vetches, Lucerne, 

 Sainfoin, and some of the Lupines. Among drugs, senna 

 is prepared from the leaves of several tropical and sub- 

 tropical species of Cassia ,- and liquorice from the root of 

 Gli/njrrhiza. cultivated largely in South Europe. Several 

 important gums (gum tragacanth, gum arable, &c.) are 

 prepared from the juice of species belonging to this Order; 

 other species yield well-known dyes, of which the most 

 important is indigo, prepared from the leaves of tropical 

 species of Indigrifera. Nor must we omit the numerous 

 species which, both in our fields and our gardens, are 

 conspicuous for their beauty — the Gorse and Broom, 

 Laburnum and Wistaria, the various Acacias and Genistas, 

 the brilliant Cliauthus, the Lupines and Coronillas. 



This great Order is divided into three sub-orders — the 

 Papilionaceie. C;i'.iaJj)iiiii';e. and Mimosess, and to the first 

 of these, the Pai)iliiiiiiiri-;r, characterized by their peculiarly 

 formed irregular (lowers — the familiar Pea- flower — belong 

 all our British species. We have in these countries 

 some seventy-two native representatives of the group, and 

 variou^s others, mostly indigenous in the adjoining parts of 

 Europe, have been introduced accidentally or deliberately 

 bv man, and have now made themselves at home among 

 the native forms. None of our plants are arboreal, but 

 the Broom, Gorse, and Genistas furnish a group of shrubs 

 dear to every lover of English landscape. The Vetches 

 and Vetchlings form a coterie of exquisitely graceful and 

 highly interesting climbing plants ; while the Clovers, 

 Medicks, Bird's-foots, and their allies constitute an im- 

 portant part of the dense low vegetation of our meadows, 

 banks, and wastes. Among our British LegmniiMsx are 

 found a remarkably interesting series of morphological 

 and physiological characteristics of varied significance, aud 



* For the use of the illustratioQS which form iTiga. 2, 3, 4, and 5, 

 the writer expresses his obhgitions to Messrs. C. Gritfin & Co. I'hey 

 are takoa from his " Opeu-Air Studies in Botany." 



pertaining to almost all the different parts of the plant. 

 These must now be briefly reviewed. 



First, as to the roots. The roots of Peas, Beans, Medicks, 

 Clovers, and others are remarkable for being the seat 

 of a highly interesting symbiotic union — a living 

 together of two organisms for their mutual advantage ; a 

 kind of mutual partial parasitism. If the roots of any of 

 these plants be examined, they will be found to be knotted 

 with small tubercles. The function of these curious 

 structures has previously been briefly referred to in 

 Knowledge (October, 1900) by Mr. H. H. W. Pearson. 

 It is found that these root-swellings are the home of 

 colonies of bacterial organisms. These lowly plants are 

 extrerael}' minute in size and simple in structure, consisting 

 of rows of cells. They increase by the production of 

 spores, or by the simple dividing of the parent. Bacteria 

 possess an important power not possessed by the 

 Leguminosce, though these are so much higher in the 

 scale of Ufe ; they can absorb that important constituent 

 of plant-food — nitrogen —directly from the air. By 

 encouraging the growth of these bacteria, then, the plant 

 has at hand a store of nitrogen which it can plunder. The 

 bacteria, on the other hand, live on the sap and cell- 

 contents of the plant which they infest ; so both derive an 

 abundant supply of valuable food-material as a result of 

 the partnership. But the existence of bacteria is not 

 necessary for the life of tlieir partners. Peas or Beans 

 grown in a sterilized soil will flourish, but no doubt they 

 have to work the harder for it. Whether the bacteria can, 

 in their turn, maintain permanent independent existence 

 does not appear to be yet known. 



From tliis curious feature of the roots of many of our 

 Leguminosie we pass to a study of their leaves. The 

 reduction in size, or practical suppression, of the leaves of 

 our shrubby species is a remarkable feature. The three 

 native species of Genista have, in lieu of the ternate 

 (consisting of three leaflets) or pinnate leaves which 

 characterize the Order, small entire ovate or lanceolate 

 leaves ; the well-known Broom has, indeed, ternate leaves, 

 but they appear ridiculously small in comjiarison with 

 those of other shrubs of similar dimensions —Brambles or 

 Willows, for example. In the Gorse, the reduction of leaf 

 is carried further, and each consists merely of an in- 

 conspicuous spine a quarter of an inch long. Studying 

 these plants one will be struck by the green colour of 

 their stems, aud thus we discover how they contrive to 

 manufacture saflicient plant-food in the absence of exjianses 

 of green leaf ; the surface of the steins take up the work 

 usually carried on by leaves. In the Needle Furze (Genista 

 anglica^, and conspicuously in the Gorse, the reduction of 

 leaf-surface is accompanied by a j)roduction of spines. In 

 the Gorse the stems are very much branched, and every 

 branchlet ends in a strong spine, its point wonderfully 

 sharp and hard. This formidable array of bayonets has 

 for its object the protection of the plant against grazing 

 animals, and its efficacy is seen in the way the Gorse grows 

 fearlessly ou upland jiastures, steadily increasing if not 

 cut down and pushing back the cattle and sheep year by 

 year. That sucli protecticm is necessary to the plant is 

 shown by the avidity with which animals will eat it if it 

 is crushed. In some parts of the country such crushing is 

 done regularly as an item of farm economy, as the 

 accoiupanyiiig photograph, taken in Co. Antrim bv my 

 friend Mr. Welch, will show. The plant then furnishes 

 excellent fodder. 



In contrast to this comparative unimportance of the 

 leaf, we have in the Vetches and Vetchlings large pinnate 

 leaves which are highly developed, aud jK)ssessed of a 

 sensitiveness aud power of movement that are most 

 remarivable. These Vetches form a group of highly 



