September i, 1883.] 



THE TROPICAL AGRICULTURIST. 



207 



of stripping in alternate layers, on -the other handj you 

 remove the whole apparatus eoutaining the alkaloids, and 

 the only places where damage can occur is at the edges 

 of the alternate layers left on the tree, and gi-eat care 

 is of course necessary in binding the tree up. The other 

 disadvantage of stripping is the damage done to the ex- 

 posed cambium, and this from two causes. 1st, Coolies' 

 carelessness iu piercing the cambium with their knives in 

 removing the bark, instead of gently raising it when ready 

 to rise. Aud the second arises out of the first, or is closely 

 coimected mth it, taking strips off trees on which the 

 bark has not renewed to a sufficient thickness to allow 

 of its being taken without injm-y to the cambium. The 

 second cause could easily be remedied by some skilled 

 person going round and marking with a patch of paint, 

 or some other easily distinguishable sign, which trees were 

 to be taken. "With proper care, trees will go on yielding 

 fine bark for many years, but mider sUciug, a fine estate 

 may be ruined, at least when mature, in four years. The 

 damage done by slicing is much greater and sooner per- 

 ceptible with crown than with red barks. "We advise cky- 

 iug all barks at as low a temperatm'e as possible, as any 

 higher temperature than 90 is siu-e to act prejudicially 

 upon the bark. Drying bark at a high temperature affects 

 absolutely the character and constitution of the alkaloids, 

 rendering the separation of the quinine a matter of great 

 difKculty, in fact fatal to the bark. — Madras Mail. 



MR. JENSEN AND THE POTATO DISEASE. 



It is much to be hoped that the protective systems 

 will be extensively tried this year, for all appearances 

 point to a severe visitation of the Potato Asease. Having 

 received several communications upon this subject from 

 l\Ir. Jensen during the past few months, and having his 

 permission to make them public, I take the present 

 opportunity of doing so. It is needless for me to describe 

 over again his system of cultm-e, beyond stating that it 

 mainly consists of giving the Potatos a second or protective 

 moulding when the first disease blotch is seen upon tlie 

 foliage, in such a manner that the uppermost tubers have 

 at least 5 inches of earth over them, at thQ same time 

 bending the top so that they hang over the furrows iu 

 a half-erect manner; the object being to protect the tubers 

 by a layer of earth from tlie spores of the parasitic fungus 

 which causes the disease. When moulded up in tlie ordinary 

 way the covering of earth over the uppermost tubers is 

 not, as a rule, more than \h or 2 mches. 



Any cause which breaks the continuity of the earth 

 covering of the tubers renders them more liable to disease. 

 Thus the presence of an earthworm at a Potato root 

 renders it more liable to have its tubers diseased than it 

 would otherwise be. An examination of 600 Potato roots 

 at Hverringe was made by Mr. H. Dreyer, for Mr. Jensen. 

 It was then found that the average number of diseased 

 tubers in the roots without earthworms was 2'2 per cent. ; 

 with one worm at each root, 35 per cent.; with two worms 

 at each root, 46 percent.; with three worms at each root, 

 58 per cent.; with four worms at each root, 71 percent. 



To demonstrate the power earth has in arresting aud 

 retaining the spores a cylindrical tube was taken, fitted 

 at the bottom with a perforated plate. In this tube was 

 placed a layer of earth 1 inch thick, which was compressed 

 to J inch, to represent the consolidation which naturally 

 takes place in the moulding of Potatos ; water was poured 

 into the top of the tube containing spores, estimated by 

 counting the number in a drop, and emi)loying the requisite 

 quantity to the number of 30,fHX). It was found that 

 about 28.000 of the spores were retained by the earth, for 

 only 2,000 ran through. The experiment was repeated, using, 

 however, 5 inches of earth compressed to 4 inches. It was 

 then found that out of the 30,000 poured in at the top 

 only one or two ran through. 



The views of Mr. Jensen upon the influence that 

 temperature exerts over the Potato disease in connection 

 with its geographical distribution are very interesting. It 

 may be stated at once that he agrees with De Rary in 

 considering that the disease is kept aUve by the my- 

 celium h ybernating and not by the agency of resting-spores. 

 Amor'irst his reasons for this view, are: — 1. Because as 

 a geitcral nde Potatos sown after Potatos the preceding 

 year are not more severely attacked by the disease than 



when they follow other crops. This he has found to be 

 the case in a great number of instances (some hun-h-ed), 

 although it is contrary to what is commonly thought iu 

 this country. 2. The date at which the Potato disease 

 first appears in any year depends, not entnely upon the 

 amount of rainfall, which of course e.xerts a powerful 

 influence, but greatly upon the quantity of infected 

 Potatos planted in spring. Last year, for instance, in 

 England. France, and Denmark the disease appeared very 

 early, aud in Denmark at least was very severe. 



Tubers attacked very early in the season will, as a 

 general rule, be rotten at the time of hfting, and con- 

 sequently the disease will have died in these tubers. The 

 "atter-sickness" ^vill be less, because the foHage, and with 

 it the fungus upon it, will have disappeared at the time 

 of lifting in such years than when the disease has com- 

 menced later. Hence fewer Potatos having the disease 

 in a hybernating state in them will be planted, aud con- 

 sequently the disease will have fewer starting points in 

 the following year. "We may, therefore, expect the disease 

 mil not be very early this year in its appearance iu 

 England, Denmark, and AN'esteru Europe, unless the 

 weather be very rainy, which will, of course, favom* the 

 rapid spread of the disease. Two very early outbreaks 

 of the disease never occur in successive years. There is, 

 upon the conti-ary, a tendency for the fii'st appearance 

 to alternate between a late and early date; as. however, 

 the weather has a great influence, this is not always so 

 observable as it otherwise would be. In Denmark during 

 the last twenty-three years the general outbreak has beeji 

 eight years early, nine years late, six years medium. Of 

 the eight early years it ha« been seven times after a late 

 year and once after a medium; of the nine late years it 

 has been four times after a medium and five times after 

 an early; of the six medium years it has been twice after 

 an early, and three times after a late, and once after a 

 medium. 



Thus we see two very early outbreaks have never followed 

 one another, but a year that should be early may be late 

 or medium from want of rain. The above has reference, 

 of course, to the time when the disease is so general as 

 to have been observed by farmers and Potato growers 

 generally. 



As a rule, it is, as before stated, only in those Potatos 

 which are infected late iu the year that the fungus 

 hybernates, those which are attacked early in the year 

 perish entirely. This year Mr. Jensen found only about 

 10 per cent, of diseased tubers which were sown in his 

 garden produced affected shoots bearing conidia. The 

 presence of conidia was detected upon the shoots a few 

 days after they had appeared above ground, and for the 

 last six weeks he has had the disease well developed iu 

 his garden, while it has not appeared in the gardens of 

 his neighbours. As shoAving the rate at which it has 

 spread from the diseased plant, he finds that till now it 

 has not advanced more than a yard in ten days. 



Now. if the outbreak of the disease was dependent 

 upon resting-spores, the fact of two early outbreaks not 

 following each other would not have been observed; ou 

 the contrary, an early outbreak one year would be most 

 likely to be followed by a slight attack in the next year. 

 A much more important (tuestion, however, or rather 

 series of questions, concerning the influence of temperature 

 has been engaging Mr. Jensen's attention, which includes 

 the following: — 1. "Where has the disease come from? 2. 

 AVhy did it not appear earlier in Europe and Nortli America 

 than about the year 1840? 3. "What is the distribution 

 of the disease throughout the globe? In what regions 

 can it never appear? AVhat hitherto uninvaded regions 

 will by-and-bye be visited by it if the importation of 

 Potatos from infested countries be not prohibited? 4. Are 

 there any means of rendering the outbreak late and 

 sporadic in infected countries, and perhaps oven of stamp- 

 ing it out altogether in the course of a few years? 



During the last year Mr. Jensen has been studying the 

 relationship existing between the temperature and the 

 disease, and he is at present engaged in preparing a memoir 

 on the subject, m French, in which these questions will 

 be dealt with fully. Concerning the origin of tlie disease, 

 Mr. Jensen believes it to have commenced in the Cordilleras 

 in the northern part of South America, where it has existed 

 from remote antiquity— as long indeed as the I*otatQS 



