Recognizing trees by their Foliage.  The oaks

The leaves of our two native species of Oak,though very similar in general form and outline, differ by distinctly marked characteristics. The leaf of the English  or pendunculate Oak has a wavy appearance and the species was once referred to as the Wavy Oak, is readily distinguished by the absence or near absence of a leaf stalk,which is distinctly possessed by the Sessile Oak,Quercus petraea, formerly referred to as the flat-leaved oak.

While the former has no leaf stem {or hardly any} the fruit {acorns} are produced on stalks,hence the alternative name of Penduclate oak,whilst the latter has leaf stalks, but the acorns sit stalk-less upon the branch giving rise to its common name of Sessile Oak sessile indicating stalk-less.

Leaves of the English oak. Note the leaves have no stalk but the acorns {just developing } are produced on long stalks.

Courtesy of Franz Xaver CC BY -SA 3.0 unported license. {Taken in Austria}

Leaves of the Sessile oak  note the leaf stalks and how the acorns sit right upon the twig without any stalks. 

Courtesy of Nenko Lazarov Creative Commons Attribution Share Alike 2.5 license.



Characteristics of the two species in respect of the foliage.

The English oak Quercus robur has a way appearance about it as previously mentioned,gives the leaf a somewhat rugged look and the large lobed margins are less regular and symmetrical than are those of the glossier,and more handsome appearance of the Sessile oak Quercus petraea.

However, now we have noted the differences of the two kinds it is also worth noting what is common to both.The particular character of venation{ the arrangement of the veins on a leaf} and the beauty of the Autumnal colouring. The leaf is traversed by a prominent and slightly wavy mid-vein,from which waved veins alternately diverge,on each side ,at an acute angle,each branch vein proceeding to the apex of a lobe. from these branches contorted veinlets run irregularly,almost at right angles,and give origin to a thick network of venules { tiny branches of veins},which anastomosing { reticulate patterning} cover the entire surface of the tissue and provide the elaborate and beautiful system by which life and vigour are carried into spreading foliage of the Oaks. 

Autumn sees the change of colour

But as on the wane of the year,the vital forces of the tree become weakened and the full deep green hue looses its hold and the mellow tints of autumn are seen on the tissue.

Plants may be said to live through drinking and breathing. Their roots with the moisture they extract from the earth absorb the chemical  substances which conduce to their life,health and beauty. Their leaves through the almost countless stomata { breathing pores} take in the carbon of the atmosphere to form their solid parts. The tree absorbs the carbon,which is rejected by all over living things, while in turn the leaves give off that one thing, other animals, including ourselves, cannot live without,oxygen.

However,out of necessity, times and seasons for the performance of this useful function is again adapted to help other living creatures.as for an example it is mostly during the day time that man is occupied outdoors,and it then that the plant world is under the influence of the sun,is giving off its oxygen,for his benefit. At night when most of us are asleep, oxygen is largely absorbed by the green parts of the leaves.

When these are performing healthy functions and are in full vigour the action of the sun causes them to part with their oxygen.But as they approach the season when they fall, their active functions of assimilation and exhalation become diminished. the oxygen breathed in at night is not freely given off during the day time and its retention in the cellular tissue  cause,under the rays of the sun,the exquisite tinting of autumn.

How much these striking effects of colour is partly dependent upon the chemical substances, other than oxygen, absorbed into the tissues of the plants from their roots towards the approach of the season of the leaf fall,along with the amount of light and warmth at that time. The presence of chlorophylle in the cellular tissues of the leaves,causes them ,under the action of light,to assume their green hue. Along with the varying presence of other pigments occasions the almost endless shades of other colours.

English oak in Autumn one of its various shades.

Courtesy of Sydmolem {Netherlands} Cc BY-SA 3.0 unported license.

Gilpin ---

Gilpin in his book 'Forest Scenery', 1700's  remarks of the oak " Of all the hues of autumn those of the oak are commonly most harmonious. As its vernal tints are more varied than other trees,so are its autumnal tints. In an oaken wood you see every variety of green and every variety of brown, owing either to the different exposure on the tree,its different soil,or its different nature,but it is not my business to enquire into the causes"

Those who have not stood beneath  the spreading boughs of an oak in early autumn and carefully looked up through the tree towards the light in such a manner as to bring it into view the various hues of the foliage,can have little idea of the almost infinite variety of tints,not only on the same tree and on the same branch but also on the same twig. 

On the same tree are the full green leaves of summer untouched by the slightest shade of autumn  colour and leaves that have reached the last shades of their colouration and between these two extremes is possible tone and shade.

Except for some accident  which has broken the branch or killed the leaves upon it there is no harsh contrast.next to the deep green summer leaves one may encounter with a slight glow of golden light, but a glow so spread upon the leafy surface as to give an indefinable sense of richness without the naked eye being able to detect where the invading hue ends or where it begins.

Others will have their leafy lobes just touched by the lighter colour as if they were under the rays of the sun,and the hue from its starting point spreads inward merging so imperceptibly with the green that it is impossible to tell the line of demarcation. Sometimes the upper half of the leaf is dyed with a russet hue which ceases mid-way giving place to the normal green or the autumn tinting may be spread in larger or smaller patches which are.so to speak, insulated by the surrounding verdancy.

From these various stages  the process of autumn tinting advances until the gold and russet or Orange and bronze, or it may be nearly red colouring has covered the surface driving out the green which tends to linger until finally extinguished.

English oak

Courtesy of Haabet Public domain






Sessile oak .

Courtesy  of Arnaud 25 Public domain.


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