IN EXTRA-TROPICAL COUNTRIES. 283 



pushes through shifting sand its spreading roots, which 

 attain a length of 70 feet. It will maintain its hold in 

 hollows of drifts where even poplars fail (Wessely). The roots 

 are poisonous. The allied R. viscosa attains a height of 40 

 feet. No less than four arborescent Robinias are recorded 

 from Juan Fernandez. 



Roccella tinctoria, Candolle. 



Canary Islands, Azores, also in Middle and South Europe and 

 North Africa. This Lichen furnishes the litmus, orseille or 

 orchil for dyes and chemical tests. It is a question of 

 interest whether it could be translocated and naturalised on 

 the cliffs also of our shores. Other dye-lichens might per- 

 haps still more easily be naturalised; for instance, Lecanora 

 tartarea, L. parella, Pertusaria communis, Parmelia sordida, 

 Isidium corallinum, and some others, which furnish the Cud- 

 bear or Persio. 



Rosa centifolia, Linne. 



The Cabbage Rose. Indigenous on the Caucasus and seem- 

 ingly also in other parts of the Orient. Much grown in 

 South Europe and South Asia for the distillation of rose- 

 water and oil or attar of roses. No pruning is resorted to, 

 only the dead branches are removed; the harvest is from the 

 middle of May till nearly the middle of June ; the gathering 

 takes place before sunrise (Simmonds). From 12,000 to 

 16,000 roses, or from 250 Ibs. to 300 Ibs. of rose petals, are 

 required according to some calculations for producing a single 

 ounce of attar through ordinary distillation. The flowers 

 require to be cut just before expansion ; the calyx is separated 

 and rejected ; the remaining portions of the flowers are then 

 subjected to aqueous distillation, and the saturated rose-water 

 so obtained is repeatedly used for renewed distillation, when 

 from the overcharged water the oil separates on a cold place 

 and floats on the surface, from whence it can be collected after 

 refrigeration by fine birds'-feathers. Rose oil consists of a 

 hydrocarbon stearopten which is scentless, and an elacopten 

 which is the fragrant principle. But some other methods 

 exist for producing the oil; for instance, it may be got by 

 distilling the rosebuds without water at the heat of a salt-water 

 bath. The odour may also be withdrawn by alcoholic distilla- 

 tion from the roses, or be extracted by the " enfl enrage' 7 

 process. The latter is effected by placing the flowers, collected 

 while the weather is warm, into shallow frames covered with a 

 glass plate, on the inner side of which a pure fatty substance 

 has been thinly spread. The odour of the flowers is absorbed 



