720 ERECT FOLIAGE STEMS. 



and many species of Australian eucalyptus. Then the membraneous bark, 

 which separates as dry films and ribbons ; this form of bark is shown in the 

 Common Birch (Betula alba), illustrated opposite. Many species of the 

 Australian genus 3Ielaleuca exhibit a bark which, when stripped from the stem, 

 looks deceptively like a thin silky material. A third form is the ringed bark, 

 which is detached from the stem in the form of thin, irregularly-fissured tubes, 

 and is especially developed in the Mock Orange (Philadelphus). A fourth form, 

 of which the Vine {Vitis vinifera) may serve as an example, is the fibrous bark 

 which is detached as numerous stiff' threads. Finally there is the fissured bark, 

 which is produced on the stems of the oak, lime, ash, and numerous other leafy 

 trees. In this form the bark is not detached in large pieces, but is niptured by 

 the increasing thickness of the stem, causing longitudinal fissures with a sinuous 

 or zigzag course, by which in one case only narrow ridges and grooves, and in 

 other cases broad angular patches are outlined. Epiphytes, especially mosses and 

 lichens, prefer to settle on fissured bark, and older stems with this kind of bark 

 are in temperate regions usually overgrown with cushions of moss, in the tropics 

 with ferns, bromeliads, and orchids. Such a colonization would be impossible in 

 bark which falls off annually, and the stems of plane trees are not only free 

 from epiphytes, but always look as if they had been scraped or peeled. 



The form of the bark is so characteristic that by it alone the species of the 

 tree can be recognized; it therefore constitutes an important feature in the picture 

 of a tree, nor can it be altered according to fancy. It is inadmissible that artists 

 should combine the studies they have made of various trees as they please, 

 perhaps putting the crown of an oak on the trunk of a plane. That the colour 

 of the bark is as important in the habit as the tint of the foliage goes without 

 saying, and it is evident that the relative sizes of the various trees round about 

 must also be considered. 



The height and age of trees cannot be represented in definite figures, but this 

 much is certain, that every species of tree, just like every species of animal, is 

 limited to a certain size and age which is but rarely exceeded. The records of 

 age which have come down to us are for the most part too great. When trees of 

 primeval forests are said to be a thousand years old, the estimates are based upon 

 conjecture, and only in rare cases on actual measurements. The celebrated Baobab 

 (Adansonia digitata) was reckoned by Adanson on the ground of the thickness 

 of the annual growth to be about 5000 years old, but whether a miscalculation 

 has not crept in must remain uncertain. The age of the celebrated Dragon Tree 

 of Orotava, already mentioned once before, has even been estimated at 6000 years; 

 the Plane of Bujukdere, on the Bosphorus, at 4000 ; and the so-called Mexican 

 Cedar (Taxodium Mexicanum) was estimated by Humboldt at 4000 years. I 

 would not like to stand security for these numbers either. On the other hand, 

 the following extreme limits of age are calculated with fair accuracy: — For the 

 Cypress (Cupressus fastigiata), 3000 years ; the Yew (Taxus baccata), 3000 ; the 

 Chestnut (Castanea vulgaris), 2000. the Oak (Quercus pedunculata), 2000; the 



