516 



THE GARDENERS' CHRONICLE 



hid 



been given off. It must, however, be 



gas, naa Deeu s .t~" — — — ■ u':„„ 



confessed that this experiment is far from being 

 satisfactory; the mere filtration of water does not 

 bv any means insure the total separation of all vege- 

 table matter. Indeed, it is plain, that any mecha- 

 nical process which does not entirely separate all 

 animalcules from the water, will also most probably 

 leave more or less vegetable matter in suspension. 



It is very interesting to read over the experiments 

 on the growth of plants, which were made more 

 than 70 years ago, by Count Rumford and Dr. 

 Priestley, in which precisely these same facts were 

 observed, and the same conclusions arrived at. It 

 was in the year 1771, that Dr. Priestley first ob- 

 served the influence of carbonic acid on growing 

 plants ; he found that air which had become noxious, 

 from the presence of putrifying animal matter, was 

 generally fatal to plants ; but that if they were not 

 at once killed by it, then they grew in a manner 

 more vigorously, indeed, than in any other sort of 

 air. This fact, he observes, led him " to conclude 

 that plants, instead of affecting the air in the same 

 manner with animal respiration, reverse the effects of 

 breathing, and tend to keep the air sweet and whole- 

 some." Seven years after this, in 1778, Dr. Priest- 

 ley discovered, that under some circumstances 

 putrefying animal flesh, when placed in spring 

 water, gradually became covered with a green filmy 

 matter, and then evolved oxygen under the influence 

 of sunshine, in place of merely giving out a mixture 

 of carbonic acid, nitrogen, and carburetted hydrogen. 

 He concluded that this green matter was of vege- 

 table origin, and that the oxygen produced was set 

 free by the growing plants, which, under the influ- 

 ence of sunshine, were able to decompose carbonic 

 acid gas. This view of the subject, was, however, 

 strongly controverted in 1787 by Count Rumford, 

 who published in the " Philosophical Transactions" 

 a number of experiments upon the evolution of 

 oxygen in water by silk, wool, and other fibrous 

 materials. He examined portions of stagnant water 

 with a microscope, and found that at the period 

 when it yielded most oxygen it contained no micro- 

 scopic plants, but abundance of animalcules. He 

 says, " The colouring matter of the water is evidently 

 of an animal nature, being nothing more than the 

 assemblage of an infinite number of very small, 

 active, oval-formed animalcules." 



These statements had been long forgotten, and 

 they have only now been again brought to light by 

 the rediscovery of the fact, or rather by the same 

 conclusion having been a second time arrived at. 

 Analogy would certainly lead us to expect that the 

 same general relation and dependance should be 

 found to exist between the lower forms of animal 

 and vegetable life, as between the more perfect ; and 

 we should, therefore, require the most full and 

 satisfactory evidence, before we could receive as a 

 fact, the statement that infusorial animalcules act in 

 air and water in the same way as plants do. It is 

 a subject full of interest, and well worthy the at- 

 tention of naturalists ; for, assuming the fundamental 

 fact to be proved, of the emission of oxygen by these 

 minute animals, it then becomes important to 

 ascertain the source whence they derive it, whether 

 from the decomposition of water, or of carbonic acid. 

 According to the views of the most recent observers, 

 it is the special office of these animalcules to aid in 

 the decomposition of dead animal matter ; just as it 

 is the province of the minute microscopic fungi to 

 assist the putrefaction of dead vegetable matter. 



We have much pleasure in announcing that the 

 late Mr. John Townsend Aiton, of Kensington, l^s, 

 by his will, bequeathed the sum of 100/. to the 



and wet, heat and cold — on the wounds of the denuded 

 branches, and the consequent destruction of the wood 

 by premature decay, accelerated by rot and parasitical 

 fungi. By the philosophical, I mean that which takes 

 cognizance of the damage which the tree must sustain 

 from the loss of its respiratory organs, inducing an 

 imperfect exhalation of the watery fluids of the sap, 

 with other analogous phenomena to be adverted to more 

 fully hereafter. To the former inquiry belong the 

 visible effects ; to the latter, such as for the most part 

 must be taken as the results of calculations from scientific 

 data. I shall first advert to the mechanical part of the 

 inquiry. 



Nothing is more common than to meet with fine 

 timber trees, when felled, presenting a hollow bole, with- 

 out — to an unpractised eye — presenting any external 

 symptoms of such a condition. There can be no ques- 

 tion that hollow trunks sometimes do occur, from causes 

 which could not possibly be indicated externally. But 

 I am confident that in numberless instances where 

 faulty timber lies concealed beneath a smooth exterior 

 of bark, a little observation on the comparative external 

 appearance of trees, in relation to the condition of their 

 trunks, will infallibly lead the observer to useful results 

 in his observations. 



I could name a plantation — Oak and Spanish Chestnut 

 mixed — of perhaps 60 years' growth, where, from exces- 

 sive pruning of the lower branches, when the trees were 

 some five-and-twenty years of age, not one-third of them 

 has a solid trunk. It needs no prophet to announce 

 this in the Chestnut, for the woodpecker, in the majority 

 of the trees, has rendered the fact patent to the most 

 casual observers. A word, en passant, in vindication of 

 this beautiful denizen of the woods, a bird which every 

 keeper persecutes to the death, whenever an opportunity 

 offers. It is urged, by ignorant woodmen, and persons 



Fig. 2. 



Fig. 1. 





7 ll, 7 a11 ^PPears fair, and thlT Ir ° m ** *> 

 what I have described will lead? **? ^fifc 

 I is no fictitious picture. \ ££ * *h* jjgjj 

 had several of its large branch?, W rge °*i£ 

 obstructed a roadway? and ?t s ^f ^ b ^A 

 that very circumstance, that h? Sode <*Mfr5 

 rains percolates through the hw ^ tet aft <* b»Z 



tint h^P Tf U ™^i5 r 16 trUnk > and find* •! **I 



tree. The annexed drawings^ If aft* *>»N 

 trations of the two conditions Thf ^ 51 

 from Nature, and are Oaks F\s l ; \i. Were *«^ 

 and if bought for a sound irunk would /oul^ ^ 

 faulty ; of fag. 2, in its free and unre.w T 8 !*• 

 there cannot be two opinions. 0. L. ^^ g*o*H, 



( To be continued.) 



BRITISH ASSOCIATION FOiTthp iTM7 



MENT OF SCnS*™ E m *S<x 



On the 

 Descent of 



Theory of the FormationTf Wt*A \ 

 the ;A* in Plants ; by Drl^ 



wood in plants, and objected to'the viewThautw'' 

 form the wood, on the ground that the li^L . i?* 



author drew attention to the theory of the f 





lurm uie wooa, on me ground that the limeoiw ,7 . 



ceij 



m 



P«t8 4 



of little observation, that it destroys the timber. Who 

 ever saw a sound tree damaged by it \ No one. It is 

 not till age or bad management has induced disease and 

 decay, that the woodpecker deigns to pursue his vocation 

 on any tree. It would be useless for him to do so. 

 Insects and their larvse are his dainties. These, lurking 

 beneath the rotting bark, and in the crevices of decaying 

 wood, he assiduously pursues. Decaying, and not 







Gardeners' Benevolent Institution, subject to the 



legacy duty. Mr. Aiton had been a supporter of u u \ * i z> * • , , , ...-*«".■ 



the charity from its commencement, and had always J^J^^ 0116 ^ Bmt f bl f localltM ? f " hlS U f ful 



exhibited much interest in its proceeding. Let us TTlv i 7 1 fi* 0n *?° ^ ° CCa91 ° n t0 S™ ? 1186 



hone that nthpr* ™», r ^;„L^* i ii 1 standing timber should consider the green woodpeckers 



nope that others may be induced to follow so good as his valuable friends. 



which were not formed in the leaves "but in Jn 

 of the plant. Wood was formed in a ll m 

 the plant where elongated cells were general , 

 independently of leaves, or the formation of leav* ' 

 m the lower part of the cut wounds of the stem* d 

 plants, in the portions of trunks left when txmJL 

 cut down, in the abortive branches formed in the 2 

 of such trees as the Elm and the Cedar, and hi q£ 

 parts of the vegetable structure. He also objecteTh 

 the theory of the formation of the ligneous or any otb 

 secretion, which might be subsequently appropriated bf 

 the cells, in the leaves alone. He maintained tint & 

 the facts brought forward to support the theory of tie 

 descent of the sap might be explained on the known bet 

 of the ready permeability of the tissues of the plat 

 He related the details of experiments performed on tk 

 species of Spurge ; in which the fluid was found toexofc 

 from the stem and branches in these plants just in m> 

 portion of the quantity of fluid contained in the pint 

 above or below the section made, and not in obediaw 

 to any law of the descent of the sap. The cells of pilots 

 were nourished in two ways : — first, by the sap contaa- 

 ing carbonic acid, ammonia, and other substances-iai 

 secondly, by materials, as sugar, gum, &c., formed i. 

 the cells. These latter were not formed solely in 4e 

 leaves, but in all cells. He regarded the leaves » 

 organs by which the water of the sap was got rid d, 

 and by this means a further supply of sap from tk 

 earth and atmosphere was insured. The way in whid 

 the demand for sap was insured might be imitated by i 

 common sponge, on the upper surface of which evapora- 

 tion went on, and the lower surface being in contact 

 with water would always supply this fluid, as a demand 

 for it was created by the evaporation above. Thil 

 phenomenon had been attributed to a specific vitality, 

 but it was unphilosophical to speak of vitality as a force, 

 when it could not be demonstrated to exist, and especially 

 when physical forces were capable of explaining tk 



phenomenon. 



Prof. Henslow said that he agreed with the views i 

 Dr. Lankester with regard to the theory of the forma- 

 tion of wood proposed by Dupetit Thouars. He 

 thought it was evident that whatever was the fun« 

 of the leaf, it did not send down the woody fibres wind 

 formed the trunk and branches of exogenous treft 

 The tracing the woody fibres up to the leaf did n« 

 prove their origin there. With regard to the desc* 

 of the sap, he did not agree with the author o m 

 paper, who, he thought, took too physical a ™ w0 \~ 

 function of the plant. The leaves were not mere orw 

 of evaporation. They performed the function ot eaj 



r „ s-iJL^^jt f heat, and depend 



He believed that the to* 

 did effect a "certain change in the juices brougjt 

 them, which changed matter was again token w- ^ 

 the system of the plant, and there being f^t^ 



tion, which was independent 

 on the vitality of the plant 



an example. 



JOTTINGS ON FOREST PRUNING * 

 I am not about to write a treatise on forest pruning 

 nor to attempt to arrange in a systematic manner what 

 I have to say on the subject ; but thinking that this 



SS^ *•> of an adult age; and to an ordinary 



and sketches in relation tWotn r *hJ C? f 1™:"?.! obs , erve r the trunk may be pronounced sound. I shall 



It sometimes happens that a tree is not sufficiently 

 hollow for the woodpecker to undertake a boring expe- 

 dition, a fact which instinct enables him quickly to 

 ascertain, although it may be useless or nearly so as 

 timber. There may be no remains of denuded branches 



to point out the fact of its having been excessively 



of lignine and the other secreted ma 'en 

 -Mr. Huxley quoted the instance of th »£ 

 and great "quantity of wood forrn^ J .. 

 kinds of Lianes of tropical fore»b 



of the formation of woo J£ 

 dently of the leaves. These plants hadju f ^ 

 a remarkably small number of leaves. 



plants.- 



growth 



various 



stances in favour 



relation thereto, I shall beg permission 

 to lay them before your readers, with the hope that 

 should they command no other notice, they will at least 

 direct attention to an ill-understood but not the less 

 important subject. 



On a casual investigation, forest pruning will be „. 

 to resolve itself into two distinct branches of inquiry 

 the mechanical and the philosophical. ~ " " 



seen 



. m , , r . . - f - - But although the 



X i h oi inquiry may be of an apparently oppo- 



ltf7% '■ ?7 * £?J°r* t0 approximate and 

 ^ h ^P^V^^ich they appeared to diverge, 

 viz., where the effect of the pruning on the health of U.e 

 tree whde mng, and on the value of the timber when 

 felled, lias to be considered By the mechanical inquiry 

 I mean all that relates to the action of weather- " 



endeavour to show how such a tree may readily be dis- 

 tinguished from that which is in reality sound. But we 

 must first see in what way the former became faulty. 

 Some 20 years ago several branches, by way of clearing 

 the plantation and rendering its bole, with that of its 

 numerous companions, a few feet more in length, were 

 cut off nearly close to where they joined the trunk. 'Some 

 of the wounds thus inflicted may have been 6 inches in 

 diameter. The wet fell upon them and 

 absorbed. Year after vear tl 



gradually 



year tins was repeated till the 



tis ues ot the wood became destroyed. Now numerous 



fungi insinuated their myceliums, and ramified amid the 



woody fibres, penetrating the medullary rays, and com- 



,„„„., | P^tmg the destruction the water had begun. Meanwhile 



bought ! l a>er a ft e r layer of new wood was being deposited on 



Gray 

 of wood, 



of the 



asm 



believed that the theorj «» -•- . Thoo < 



, - •— by Du Hamel, W"^ 



and others, was no longer tenable. i» ^ « 



vessels from cells could be easily oDS " b£t ' ff e«n* 

 exogenous plants there was no vacant Bpw {( ]<,« 

 wood and the bark for the woody fibres to o ^ $ 

 through. Even in the spring of the year, ^ * 

 was passing most rapidly between the » o ^ 

 bark, the organic connection was comp^ do(rn 

 matter was elaborated in the leaves *? " fnrt her «*" 

 the plant he was not prepared to say, ^ qUote d s«J 

 riments were desirable. — vr. * ^ e n iaten» 



experiments which bethought proved «'' d iB # 

 of the growth of the plant were not px^ ^ i 

 leaves.— Dr. Lankester replied, ana -^ rf P 

 present it appeared to him that the ^ ^ 



preparation of gum or any othei seer ^ rf w 



I which was found subsequently in any 





