GEOGRAPHICAL DISTRIBUTION OF PLANTS. 549 



5. Meadow and pasture plants, as a great number of grasses and trefoils. 



6. Plants found in cultivated fields. In this division many plants are included which 

 have been introduced by man along with grain ; as centaurea cyanus, corn blue-bottle, 

 sinapis arvensis, or common wild mustard, agrostemma, corn-cockle, several species of 

 veronica, or speedwell, and euphorbia, or spurge. 



7. Rock or wall plants ; as saxifrages, wall-flower, some species of sisymbrium, or 

 hedge-mustard, bromus, or brome-grass, linaria cymbalaria, or ivy -leaved toadflax. 



8. Sand plants, as carex arenaria, or sea-carex, calamagrostis arenaria, or small sand- 

 reed, and plantago arenaria, or sand plantain. By the cultivation of these plants, large 

 districts have been reclaimed from utter barrenness, and clothed with stately forests ; and 

 countries subject to a periodical invasion of sand, blown over them by the prevalence of 

 certain winds, have been rescued from that calamity one of the most useful agricultural 

 enterprises of modern times. The plan was first adopted by an engineer of the name of 

 Bremontier, on the coast of Gascony. He sowed, in the driest and most shifting sand, 

 the seeds of the broom, genista scoparia, mixed with those of the sea-pine, pinus mari- 

 tima, and then covered over the spaces that were sown with branches from the nearest 

 pine forests, by which means the sand was to a certain extent prevented from shifting. 

 The broom, which springs up first, serves the double purpose of further restraining the 

 sand, and of nursing the young pines ; and the foliage of the latter, after a growth of 

 seven or eight years under shelter of the broom, becoming annually mingled with the 

 sand, tends to fertilise it. After this period the pine overtops the broom, and frequently 

 entirely kills it with its shade. In ten or twelve years the rising forest is thinned for the 

 manufacture of tar, and for procuring branches to cover the newly-sown districts. After 

 twenty years have passed, a fall of the trees commences for the manufacture of resin. 

 Thus these forests, placed on the dunes or drifting sand-hills between the mouths of the 

 Adour and the Garonne, shelter the whole country behind them from the inroads of the 

 element from the sea, and yield themselves a supply of an important article of commerce. 



9. Plants found on rubbish, or those which select the habitations of man and animals, 

 on account of the salts and azotised substances which enter into their composition, as 

 pellitory of the wall, nettles, and some mushrooms. 



10. Forest plants, including trees which live in society, as the oak, beech, elm, and fir, 

 and the plants which grow under their shelter, as the greater part of the European 

 orchises. Some of the former attain to enormous dimensions, and survive to a hoar 

 antiquity. Four celebrated yew trees in Great Britain, whose dimensions are on record, 

 appear, from the number of concentric zones observable in a transverse section of their 

 stems, to have lived respectively 1214, 1287, 2558, and 2880 years. In relation to the 

 first of these examples, we have the testimony of history, that this tree was in existence, 

 and must have been of considerable size in the year 1133, it being recorded that the 

 monks took shelter under it during the building of Fountains' Abbey. De Candolle 

 gives the following ages, but is supposed to have overrated them one-third : 



Elm ... of 335 years 



Cypress - about 350 



Cheirostemon - - about 400 



Ivy .... 450 



Larch .... 576 

 Orange - ... 630 



Olive .... 700 



Oriental Plane - - 720 years and upwards 



Cedar of Lebanon - about 800 



Oak - - 810; 1080; 1500 



Lime ... 1076; 1147 



Yew . . 1214; 1458; 2588; 2880 



Taxodium - . 40OO to 6000 



Baobab ... 5150. 



The majestic forests of the equatorial zone contain trees of a most gigantic size. On 

 the banks of the Atabapo, a bombax caiba was measured by Humboldt, more than 120 

 feet high, and 15 feet in diameter ; and near the village of Turmero, to the south-west 



