48o 



NATURE 



[September i6, 1897 



Several such forms have now been obtained, the observations 

 of Burri and Stutzer that certain of the commonest bacteria of 

 the alimentary canal — e.g. B. colt commune — abounding in fresh 

 manure, are especially active, being particularly suggestive. 

 You will thus notice that we have now a sketch of the whole of 

 the down-grade part of the cycle of organic nitrogen in nature ; 

 it only needs supplementing by the history of the fixation of free 

 nitrogen from the atmosphere by leguminous plants and certain 

 soil-organisms to complete the sketch. 



As is well known from investigations in which Eriksson, 

 Woronin, Frank, Prazmowski, and others, including myself, 

 have taken part, the nodules on the roots of leguminous plants 

 contain a fungus — the morphological nature of which is in 

 dispute — living in symbiotic union with the protoplasm of the 

 cells. Hellriegel and Wilfarth showed in 1888-90 that, pro- 

 vided the root-nodules are present, these leguminous plants fix 

 the free nitrogen of the atmosphere ; and Laurent and Schloesing 

 put this beyond all doubt in 1892 by demonstrating that a closed 

 atmosphere in which Legumrnosic grow loses nitrogen in propor- 

 tion as the plants gain it. Meanwhile Schulz Lupitz had shown 

 that agricultural land poor in nitrogen can be made to ac- 

 cumulate it in paying quantities by growing lupines on it, and 

 quite recently pure cultures of the organism of the nodules have 

 been placed on the market underthe unfortunate name. Nitragin. 

 It is claimed that these organisms can be readily used in 

 practice to inoculate the seeds or soil. 



Kossowitsch in 1894 showed that certain symbiotic unions of 

 algre with bacteria are also capable of fixing nitrogen ; and 

 Winogradsky declares that there "exists in the soil a bacterium 

 which, provided it is kept protected from oxygen by aerobic soil 

 organisms, can itself do this. We are quite unaware of the me- 

 chanisms here concerned ; but in all cases it appears certain that 

 active destruction of carbohydrates is an essential condition, and 

 we can only assume that the nitrogen is forced into synthetic 

 union by means of energy derived from this destruction. Here, 

 then, we have a glimpse of the up-grade part of the cycle of 

 nitrogen in nature, the importance of which to agriculture cannot 

 be overrated. As to the theoretical bearings of the matter, we 

 are still much in the dark, and can only anxiously await the 

 results of further investigations into the nature of the peculiar 

 fermentations and their products going on in these nodules. I 

 now want to draw your attention to a bearing of the above dis- 

 coveries concerning denitrifying bacteria on some agricultural 

 and horticultural questions. 



It is well known that a gardener eschews the use of fresh 

 manure. Why is this ? The most obvious reply might seem to 

 be, because the ammonia compounds and other nitrogenous 

 constituents in such manure are not directly useful, or are even 

 harmful to the roots of the plants. Some recent researches 

 suggest that the matter is more complex than this. 



It has not unfrequently happened that a farmer, finding him- 

 self short of stable-manure, has made up the deficit by adding 

 some such artificial manure as ChiH saltpetre, his argument 

 running somewhat as follows : — Both are good nitrogenous 

 manures, the one acting slowly, the other rapidly, so that a 

 mixture of both should be better than either alone. The results 

 have disappointed him, and numerous experiments in Norfolk, 

 as I am informed by Mr. Wood, and in the North of England, 

 as Dr. Somerville assures me, have shown that most disastrous 

 results ensue if such mixtures are used, whereas if the farmyard 

 manure is employed at first — the " shorter" the better — and the 

 nitrates applied later on as a " top-dressing," excellent crops 

 follow. The explanation seems to come from some recent ex- 

 periments by Wagner, Maercker, Burri and Stutzer, and others. 

 The farmyard manure, especially if fresh, so abounds in denitri- 

 fying bacteria that they destroy the nitrates rapidly and com- 

 pletely, free nitrogen escaping. Curiously enough, a very active 

 denitrifying bacillus was found on straw, and we know that straw 

 abounds in such manures. 



I did not intend to go so far into agricultural details as this, 

 but it was impossible to resist these illustrations of the splendid 

 field of mycological research which here lies before us. 



Nor can I avoid instancing at least one more example of the 

 organisms at work in manure. We all know what enormous 

 quantities of cellulose are manufactured daily, and even hourly, 

 by the activity of green leaves ; and when we reflect on the 

 millions of tons of dead-wood, straw, fallen leaves, roots, &c., 

 which would accumulate every year if not destroyed, we see at 

 once how important is the scavenging action of the moulds and 

 bacteria which gradually reduce these to carbon-dioxide and 



water, setting these gases free to enter once more into the cycle 

 of carbon, oxygen, and hydrogen in nature. 



In 1890 Van Senus obtained two bacteria, one an aerobic 

 and the other an anaerobic form, which in symbiotic union 

 were found to excrete an enzyme which dissolved cellulose. 

 Such a cellulose-dissolving enzyme I had myself isolated 

 from the Bolrytis of the lily disease in 1888. In 1895 

 Omeliansky, working with river mud, found an anaerobic 

 bacillus which dissolves paper with remarkable rapidity. I can 

 only hint at the importance of these forms in connection with 

 the production of marsh gas in swamps, the question of the 

 digestion of cellulose in herbivorous animals, the manufacture 

 of ensilage, and the processes of " shortening " of manure ; and 

 it is clear they have much to do with the destruction of 

 paper, &c., in sewers and refuse-pits. Moreover, their further 

 investigation promises a rich harvest of results in explanatior> 

 of the rotting of stored tubers, certain diseases of plants, and 

 several theoretical questions concerning anaerobi.sm, butyric 

 fermentation, and, possibly, that extremely difficult question on 

 which Mr. Gardiner has done such excellent work, the nature 

 of the various celluloses and constituents of the cell-wall. 



I now turn to the subject of fungus epidemics, of world-wide 

 interest, if only because the annual losses to agriculture due 

 to epidemic diseases of plants amount to millions of pounds- 

 sterling. 



The history of wheat-rust can be traced to Genesis, and at 

 least five references to it exist in the Old Testament. The 

 Greeks <vere familiar with it, and the Romans had a special 

 deity and special ceremonies devoted to it. References can be 

 given to it in old Norman times, and Shakespeare can be 

 quoted as acquainted with it. 



According to Loverdo, a law iexisted in Rouen in 1660, 

 authorising the pulling up of barberry bushes as in some 

 mysterious way connected with rust, and in 1755 the celebrated 

 Massachusetts law was promulgated. Eriksson refers to an 

 English farmer destroying his neighbour's barberry in 1720. 



The words Rohigo, Rubigo, Rotiille, Rtiggine, Rtifus, and 

 Rtist comprise a history in themselves, into which, however, 

 we have not time to go, and there are many fascinating points 

 in the history of wheat-rust which must be passed over. 



Felice Fontana in 1767 probably made the first scientific 

 investigation of rust ; he distinguished the uredo- and puccinia- 

 stages under other names, and even thought of them as rootless 

 plants exhausting the wheat ; in this, and his conviction that 

 no remedy was possible until a careful study of all phases of the 

 disease had been made, he was far ahead of his times. 



Jethro Tull, Marshall, and Withering are the most con- 

 spicuous English names in connection with this question and 

 period, and Marshall in 1781-84 experimented intelligently 

 with barberry and wheat inter-planted. 



Persoon in 1797 gave the name Fticcinza graminis to the 

 fungus. In 1805 Sir Joseph Banks described it, and suggested 

 that the germs entered the stomata : he also warned farmers 

 against the use of rusted litter, and made important experiments 

 on the sowing of rusted wheat-grains. 



A great discussion on the barberry question followed, in 

 which Banks, De Candolle, Windt, Fries, and others took part. 

 Fries particularly insisting on the difference between JEcidiiivt 

 berberidis — a name conferred by Gmelin in 1791 — and Puccinia 

 graminis. 



De Candolle had also distinguished Uredo rubigo-vera in 

 181 5, and Schmidt soon after described a third wheat-rust — 

 Uredo glumanmi. 



Matters were at about this stage when Tulasne confirmed the 

 statement of Henslow — one of my predecessors in Cambridge — 

 that the uredo- and puccinia-stages really belong to the same 

 fungus, and are not, as Unger asserted, mixed species. 



Then came De Bary and his classical investigation of the 

 whole question in 1860-64. He proved that the sporidia of 

 some Uredinea; (e.g. Coleosporiuni) will not infect the plant 

 which bears the spores, and that the recidia of certain other 

 forms are only stages in the life-history of species of Uromyces 

 and Puccinia. 



In 1864 Do Bary attacked the question of wheat-rust, and 

 by means of numerous sowings of the teleutospores on barberry 

 proved beyond doubt that they bring about its infection. 



But De Bary did more. For the first time in history he saw 

 the entrance of the infecting tube and the beginning of its 

 growth in the tissues. In 1865 he demonstrated in the same 

 faultless way the infection of the cereal by means of the recidio- 



NO. 1455, VOL. 56] 



