September i6, 1897 



NATURE 



479 



In the first place, there are several different fungi concerned — 

 those on cupulifen^ and pines, apparently mostly Tuberacea and 

 Gasteromycetes, and allied forms, being different from those in 

 orchids, some at least of which appear to be Nectrias or related 

 genera. 



The physiological relations of the root to the fungus must be 

 different in details in the case of non-green, purely saprophytic 

 plants, like Neottia, Monotropa, &c. , and in that of the green 

 plants like Erica, Fagus, Pinus, &c. 



It is well known that ordinary green plants cannot utilise 

 vegetable debris directly, whereas trees in forests appear to do 

 so ; this in appearance only, however, for the fungi, yeasts, 

 and bacteria there abounding are actively decomposing the 

 leaves and other remains. 



Now it is possible that the mycorhiza theory is not applicable 

 in all cases, and that, sometimes, what happens is this. The 

 trees, once well established, make so good a fight that in spite 

 of the leaf-decomposing fungi attacking their roots parasitically, 

 or merely ensconcing themselves in the dead primary cortex as 

 it is sloughed, they manage to keep going and to obtain such 

 shares of the nitrates and other products due to the fungus- 

 action as satisfy their needs. But although there may be some- 

 thing to be said for this view as regards a few forest-trees, it is 

 not easy to see how it would apply to the non-assimilating 

 humus-plants like Neotlia, Monotropa, &c., and we may 

 probably regard the two sets of cases as standing or falling 

 together. 



No treatment of this subject would be complete ' without 

 reference to those obscure cases of symbiosis — as we must regard 

 them — between certain algte which occur in the cavities of the 

 leaves of AzoUa and in Gunnera, and those found in the inter- 

 cellular spaces of cycad-roots. When we know more of the 

 physiology of these blue-green algae, it may be possible to 

 explain these puzzles, but at present they are mysterious 

 curiosities. 



A class of pseudo-symbiotic organisms is being more and 

 more brought into the foreground where the combined action 

 of two symbionts results in death or injury to a third plant, 

 whereas each symbiont alone is harmless, or comparatively so. 



Some time ago Vuillemin showed that a disease in olives 

 results from the invasion of a bacillus (5. olea:), which, how- 

 ever, can only obtain its way in the tissues through the passages 

 driven by the hyphae of a fungus {Chatophoma). The resulting 

 injury is a sort of burr. Vuillemin has this year observed the 

 same bacillus and fungus in the canker burrs of the ash, and so 

 confirms Noack's statement to the same effect 



Among many similar cases, well worth further attention, the 

 invasion of potato-tubers by bacteria, which make their way 

 down the decaying hyphee of pioneer fungi, may be noted. I 

 have also seen tomatoes infected by these means, and have facts 

 showing that many bacteria which quicken the rotting of wood 

 are thus led into the tissues by fungi. 



Probably no subject in the whole domain of cryptogamic 

 botany has wider bearings on agricultural science than the 

 study of the flora and changes on and in manure and soil. 



As vegetable physiology and agricultural science progressed, 

 it became more and more of primary importance that we should 

 learn what manure is composed of, what changes it undergoes in 

 the soil, and what the roots of plants do with it. Chemistry 

 did much to solve some of the earlier problems, but it soon be- 

 came evident that it only raised new questions which it could 

 not solve ; and it was not till the sequence of changes induced 

 by the successive growths of Miicor, Pilobohis, Coprimis, 

 Ascobolus, and other moulds and fungi of various sorts, followed 

 by bacteria and yeasts, began to be understood, that anything 

 approaching a coherent account of the complex phenomena 

 going on in soil or in a manure-heap could be attempted. Not 

 that all the difficulties have been solved even now, but we are 

 at least able to trace some very important chains of occurrences 

 which throw light on many hitherto obscure matters going on 

 in the field. 



Since Pasteur in 1862, and Van Tieghem in 1864, showed 

 that certain bacteria are concerned in converting urea to 

 ammonium carbonate, much has tieen learnt, and we now know 

 from the investigations of Miquel, Jaksch, Leube, and others 

 that numerous urea-bacteria exist ; and Miquel, in 1890, 

 isolated an extremely unstable enzyme — urase — which converts 

 sterile urea to ammonium carbonate very rapidly, a discovery of 

 considerable interest, as it was one of the first examples of this 

 class of bodies to be examined ; and when we reflect on the 



enormous quantities of urea which have to be destroyed daily, 

 and that fresh urine is in effect a poison to the roots of higher 

 plant, some idea of the importance of these urea-bacteria is 

 obtained. The necessity for preventing the losses of this 

 volatile ammonia by fixing it in the soil and presenting it to the 

 action of the nitrifying organisms is also obvious. 



Winogradsky's classical isolation and cultivation of bacteria 

 which take up these ammonia compounds and oxidise them to 

 nitrous and to nitric acids in the soil, may be quoted as further 

 instances of the bearing of bacteriological work on this depart- 

 ment of science, as explaining not only the origin of nitre-beds 

 and deposits, but also the way the ammonia compounds fixed 

 by the soil in the neighbourhood of the root-hairs are nitrified 

 and so rendered directly available to plants. 



The theoretical explanation of many questions connected with 



the washing out of nitrates from fallows, the advantages of 



autumn and winter sowing, and processes occurring in the upper 



soil as contrasted with subsoil, has been rendered much easier by 



these researches ; moreover, as is now well known, they brought 



to our knowledge a startling instance of the assimilation of 



carbon-dioxide by these non-green plants — bacteria — which not 



only take some of the purely inorganic ammonia, but by means 



of energy set free by its oxidation obtain their carbon also by 



breaking up the carbonate — a true case of the assimilation of 



carbon-dioxide by a plant devoid of chlorophyll and without the 



direct aid of light. Indirectly, it is true, the source of the 



energy is the light of the sun, because the oxygen employed by 



I these aerobic forms has been liberated by green plants in the 



i last instance ; but the case is none the less a startling and im- 



i portant contribution to physiology, and Winogradsky's work, 



[ which had been preceded by investigations in England by 



I Warington and others, affords one of the best illustrations I know 



of the importance of this branch of botanical investigation. 



Stutzer and Hartleb's recent publications go to show that the 

 nitrifying organism is a much more highly developed and com- 

 plex form than has hitherto been suspected ; that it can be grown 

 on various media, and exhibits considerable polymorphism — 

 for instance, it can be made to branch, and show the character- 

 istics of a true fungus, statements confirmed to a certain extent 

 , and independently by the even more recent work of Rullmann ; 

 and it appears that we have much more to learn of the morpho- 

 logy of this widely-spread and interesting plant. 



It is impossible to go into the controversy between the ob- 

 servers referred to and Winogradsky, the discoverer of the 

 j definite nitrifying organism ; but there is one point I must just 

 ! mention : if Stutzer and Hartleb's details are confirmed we have 

 j here the most remarkable case of polymorphism I know of, for 

 they claim characters for their fungus which prevent our putting 

 it into any existing group. 

 ; I have for some time insisted on the fact that river-water con- 

 tains reduced forms of bacteria — i.e. forms so starved and so 

 altered by exposure to light, changes of temperature, and the 

 low nutritive value of the river-water, that it is only after pro- 

 longed culture in richer food-media under constant conditions 

 that their true nature becomes apparent. Now, Stutzer and 

 Hartleb show that the morphological form of the nitrifying 

 organism can be profoundly altered by just such variations in 

 the conditions as the above, and occurs as a branched mycelial 

 form, as bacilli or bacteria, or as cocci of various dimensions 

 according to conditions. 



These observations, and the researches of Zopf, Klebs, and 

 others on variations in form (polymorphism) in other fungi and 

 bacteria, open out a vast field for further work, and must lead 

 to advancements in our knowledge of these puzzling organisms ; 

 they also help us to explain many inconsistences in the existirig 

 systems of classification of the so-called "species" of bacteria 

 as determined by test-tube cultures. 

 1 But the urea bacteria and the nitrifying organisms are by no 



means the only forms found in manure and soils. 

 ' In 1868 Reiset found evidence of a reduction of nitrates in 

 1 fermenting beet-juices, and in 1873 Schloesing found that free 

 I nitrogen escaped in certain soil-fermentations. Further work 

 [ by Mensel, Deherain, and others led to the suspicion that 

 ' certain bacteria can undo the work of the nitrifying organisms, and 

 in 1879 Warington showed that both nitrites and nitrates occurred 

 ' in his soil-fermentations. 



In 1886 Gayon and Dupetit put this almost beyond doubt, 

 ' and in 1891 Cliltay and Aberson isolated and cultivated a deni- 

 trifying bacterium, capable of completely reducing nitrates with 

 evolution of free nitrogen, provided it is cultivated anaerobically. 



NO. 1455, VOL. 56] 



