138 



THE GENESEE FAR^tfER. 



"Beyond all reasoiinV)le doubt, it is proved that 

 the potato never rots without the fungus, and that 

 it always rots with it. Planting the fungus on a 

 sound potato develops the disease. Sliielding the 

 potato from the fungus ])revents the disease. The 

 rot starts where the fungus begins to grow. Each 

 microscopic cell of the tuber becomes discolored 

 and rotten, when, and only when, the fungus issues 

 its branches into it, or into its immediate neighl)or- 

 hood. Constitution, tuber, propagation, aphides, 

 salt, manures and weather have nothing to do with 

 the disease, except as they favor or destroy tlie 

 fungus. 



"This is a grand result, if true. After carefully 

 studying the evidence, it is hard to reject the doc- 

 trine. Let us examine the evidence and judge for 

 ourselves. 



"As is -well known, the first indication of potato 

 disease is the blight of the leaf. This comes on so 

 suddenly, and often so peculiarly, as to point with 

 the utmost directness to a fungus as its cause. 

 That a fungus is developed on and in the blighted 

 leaf, is ))ert'ectly understood, and has been from the 

 tirst. To prove that this fungus invariably pre- 

 cedes, and is itnmediately followed by the blight, 

 is The capital achievement lately made by pr. 

 Speerschneider, and confirmed by KuiiN and De 

 Bakt, botanists of Germany. These investigators 

 have not merely looked at the blighted leaves and 

 seen the fungus tlie^-e, but have watched the fungus 

 as it rapidly sends out its branches into the still 

 fresh and healthy portions of the leaf, and liierally 

 devours them — appropriating their juices to its own 

 nourishment, and leaving behind a disorganized 

 and decayed mass as the track of its desolation. It 

 is easy to see with the unaided eye, that the fungus 

 travels over the potato leat lefore the blight. If 

 tlie observer carefully regards one of the brown 

 blight-spots when the disease is spreading, he will 

 see that at its borders, and extending over upon tlie 

 still gr<.-en leaf, is a forest of tiny mold-plants which 

 oover the leaf with a greenish down. This is the 

 ]»f>tato fungus, the Peronospora infestans, as it is 

 now botanically designated. 



" The manner of growth of this plant must be 

 known before one can understand its effects. It 

 comes from a seed or spore of microscopic dimen- 

 sions, a minute oval, somewhat fiattened body 

 wliich bears at either extremiry a hair-like pro- 

 longature. These spores are produced to the num- 

 ber of 13 — 16, together, in a spore-sack at the ex- 

 tremity of a branch of the fungus. They are kept 

 in a peculiar rapid motion by the vibration of the 

 hair-like appendages, and when ripe they burst the 

 spore-sack and are discharged. Their motion con- 

 tinues about half an hour, when it becomes slower, 

 aud shortly ceases. Then the 8[)ore begins to 

 change its "figure, the hairs disappear, and sliortly 

 a thread like branch begins to protrude from its 

 side; this rapidly increases, and if the spore is 

 upon the potato plant, the branch, wliioh is tlie 

 seedling fungus, so to speak, penetrates the tissues 

 of the potato— li'af, stem or tuber, as tlie case may 

 be — and forthwith commences its para.sitic life. The 

 yoimg fungus buds out in various directions, send- 

 ing into tlie juices and ci-lls of the |)otato its feed- 

 ing branches or mycelium ; wliile other, or fruit- 

 branches, pass out into the atmosphere and reju-o- 

 d«c« spores with marvelous fecundity. The growth 



of the mother plant continues as long as it finds 

 food and the requisite warmth and moisture. "When 

 the siip]dies existing in one place are exhausted, 

 the plant dies in that spot ; but the branches which 

 had previously extended into the neigliboring re- 

 gions, continue to grow, so that the devastations 

 of this fungus are like a fire which spreads in all 

 directions wlierever it finds fuel. 



"Nothing can explain the fact that a field which 

 yesterday was green and to all apijearance healthy, 

 to-day is black with blight, except the almost mag- 

 ical increase of this parasite. Nothing else can 

 enable us to comprehend how a part of a field — a 

 streak across it — is blighted, while the rest is un- 

 damaged. 



" De Bary has produced the blight on healthy 

 potato leaves by sowing the spores and causing the 

 'fungus' to develop on them. To accomplish this 

 it is only necessary to bring a spore in a droplet of 

 water that is stationed on a bit of potato leaf, or 

 to keep the spore and leaf in a sufficiently moist 

 place for a few hours, to see with the microscope 

 tlie fungus develop and the leaf turn yellow and 

 finally brown, with all the symptoms that are ob- 

 served when the disease is taken in the natural 

 way. 



" By these observations and experiments it ap- 

 pears proved beyond all cavil that t\\e Peronospora 

 infestans is the cause of*the leaf blight, which is 

 the invariable precursor of the rot ot the tuber. 



"The question next comes np: Wii.at has the 

 fungus to do with the rot itself — with the potato 

 disease proper ? 



" On this point the evidence is no less conclusive. 

 Dr. De Bary* describes the following simple expe- 

 riment, which demonstrates that the tuber rot is 

 the work of the fungus. A perfectly healthy po- 

 tato is well waslied and cut into halves. Each 

 half is placed in a separate saucer, with the cut 

 surface uppermost, and is covered witii a tumbler 

 or bell-glass, to protect it from dust aud disturb- 

 ance. A little pure water is placed in each saucer 

 to keep the potato from drying away. 



" Upon the cut surface of one of the pieces a 

 number of spore-sacks of Peronospora are scat- 

 tered, care being taken that none shall get across 

 to the other piece. Both are now left to them- 

 selves, protected by the bell-glasses, and ui.der tlie 

 same conditions of ti.mperature, moisture. &c. In 

 ten or more days, according as the weather is 

 warmer or co'der, the experimenter may ob.serve 

 that the half upon which the spores wt-re sown 

 begins to exhibit decided symptoms of the disease, 

 while the other half remains [)erfect,ly healtliy. 

 The symptoms are [irecisely those which are always 

 ob-erved in the potato rot. The surface of the 

 tuber first turns brown at the points where the 

 spores were deposited; the discoloration extends 

 outward froir these spots in all directions, and in a 

 thw days the whide section is brown to the average 

 depth of one-half to one line. The cliange pro- 

 ceeds from the edges of the cut surface under the 

 skin of the tuber, until the whole mass is enveloped 

 in a brown coating. 



"The disease penetrates deeper and deeper into 

 the tuber, until the latter is completely infected. 

 If much moisture be present, the mass <]issolves to 



• In t>i5 work, " Die geeenwneriif; hfrnichcDde Kartoffel-Kranli- 

 hcit; Uire Unacbe uad ihre Verhuetung.'* 



