THE FARMEKS" REGISTER. 



357 



sure to light within certain limits, and feeble, in ! 

 proportion to their removal from It ; till, in loial | 

 and continued darkness, they arn entirely dediuule j 

 of green secretion, and become blanched or eiio- ' 

 lated. The same result uiiends all thi-ir oiher 1 

 secretions ; timber, gum, sugar, acids, starch, I 

 oil, resins, odors, Havors, and all the numberless i 

 narcotic, acrid, aromatic, pungent, astringent, and 

 other priuciples derived Irom the vegetable king- 

 dom, are equally uiHuenced, as to quantity ami 

 quality, by the amount of light to which the 

 plants producing them have been exposed. 



76. it is, however, to be observed that, as has 

 already been stated (68), the capability ol plants 

 to bear the action ot direct light varies according 

 to their specific nature. One species is organized 

 to suit the almospliere of a dense wood, into 

 which ditluse light only will penetrate ; another 

 is planted by nature on the exposed lace of a 

 sunburnt rock, upon which the raysolashadeless 

 sun are daily sinking ; in these cases, the light 

 which is necessary to the one would be destruc- 

 tive of the other. Ttie organic ditlerence of such 

 species seems to consist chietiy in the epidermis, 

 which regulates the amount oi perspiration (,61). 

 It is theretcjre to be remarked, that it is not the 

 greatest quamiiy of light which can be obtained 

 itiat is most lavorable to the healthiness ol plan's, 

 but the greatest quantity they will bear wiihoui 

 injury. If the former were true, the concentrated 

 lighi of a lens would be better than the strongest 

 ordinary light ; but the etl'ect of the concentrated 

 light ol a iens is to burn the surlace, and the or- 

 dinary solar rays produce the same etiect upon 

 many plants, probably by exhausting the tissue 

 of its water laster than ii can be supplied Irom 

 the roots. 



In the course of time, a leaf becomes incapa- 

 ble of perlbrnnng its luiicfions ; iis passages are 

 choked up by the deposite of sedimentary matter ; 

 there is no longer a free communication between 

 its parenchyma and that of the rind, or between 

 its veins and the wood and liber. It changes 

 color, ceases to decompose carbonic acid, absorbs 

 oxygen instead, gels into a morbid condition, and 

 dies: it is then thrown otf. This phenomenon, 

 which we call ihe fall of the leaf, is going on the 

 whole year round, except mid-winter, in some 

 plant or other. Those which lose the whole ul 

 their leaves at the approach of winter, and are 

 called deciduous, begin, in lact, lo cast their leaves 

 within a few weeks alter the commencement ol 

 their vernal growth ; but the mass of their Ibli- 

 age is not rejected till late in the season. Those, 

 on the other hand, which are named evergreens, 

 part with their leaves much more slowly ; re- 

 tain them in health at the time when the leaves 

 of olher plants are perishing ; and do not cast 

 them till a new spring has commenced, when 

 other trees are leafing, or even later. In the 

 latter class, the functions of the leaves are going 

 on during all the winter, although languidly ; 

 they are constantly attracting sap li-om the earth 

 through the spongelets, and are, therefore, in a 

 state of slow but continual winter-growth. It 

 usually happens that the perspiratory organs ol 

 these plants are less active than in deciduous 

 species. 



78. In general, a leaf is an organ of digestion 

 and respiration, and nothing more ; some leaves 

 have, however, the power of forming leaf-buds. 



if placed in or upon eqrth, under suitable cirrnm- 

 staiiccs. The BryophylUim calvciniirri lonus 

 buds at the iiidentaiions uf its nmrgin ; Malaxis 

 paludosa throws off youn<j bnils Irom lis niarirm ; 

 Tellinia grandillora occasionally hmls at tht- mar- 

 gins of I's leaves : the same tliiiii^ happens to 

 many ferns ; atid several other cases are known. 



SOME REMARKS UPON THE DISEASE, CALLED 



THE "yellows," which attacks the 



PEACH TREE. 



From the Magazine of Horticulture. 



I have noticed occasional upeful remarks on the 

 best varieties and the culture of fruit trees in your 

 valuable Magazine; but I have not, as yet. seen 

 any remarks upon the disease called the yellows, 

 which affects the peach tree, or reasons assigned 

 for its prevalence. If the cause could be Ibund 

 out, it might lead to a cure, which would render a 

 lasting benefit to our country. However valuable 

 most other fruits are, none are equal to the peach 

 in delicious flavor and healthiness, and I should 

 therefore be pleased to see this subject carefijily 

 investigated, and the experience of some of your 

 intelligent correspondents communicated through 

 your pages. 



And as I have, for about thirty years, occasion- 

 ally had my attention drawn to this subject, I am 

 willing to throw in my mite of experience, 1 ain 

 fully satisfied that the complaint exists. Some 

 persons say ihat the worm at the root is the cause 

 of the yellows, 1 acknowledge that any disorder 

 that destroys the trees will cause the leaves to 

 turn yellow, but the complaint I call the yellows 

 will kill a whole orchard, without any visible 

 wounds, on or belbre the third or fourth full crop. 

 I think where any neighborhood abounds with 

 peach orchards, it will be nearly impossible to 

 keep clear of the disease. 



On planting out young peach trees on the side 

 of a peach nursery, two years after the nursery 

 was removed, and although the ground was in 

 other respects well suited for the growth of the 

 peach tree, yet by the next autumn many of 

 them were dead, and the balance so sickly that I 

 had ihem all dug up, and there was no sign of the 

 worm at the roots. From this, and other similar 

 experiments, I think the disease may be generat- 

 ed by planting in or near where a nursery or or- 

 chard of peach trees has been, or where the laiter 

 is ; consequently, where a neighborhood abounds 

 with peach trees, there is danger of its becoming 

 overspread with disease, without greater care than 

 is usually taken to prevent it. 



I think I have seen evidences of its being in 

 some degree contagious. Richard Cromwell, the 

 respectable and worthy peach raiser, nearBalii- 

 more, has for upwards of thirty years supplied 

 that city with peaches of the best quality, on a 

 large scale. Some time since, when I was walk'- 

 ing with Mr. Cromwell through his peach or- 

 chard, when the trees were hanging full of ripe 

 Iruit, he pointed out a tree that he said had the 

 yellows, having a full crop upon it, at that time 

 worth one dollar per peck, and lo me it appeared 

 healthy; but he observed to me, "as soon as 

 I take the fruit from the tree, I shall dig it up, in 

 order to prevent the disease speading any farther, 



