478 



NA TURE 



[September i6, 1897 



rendering uniform and certain this at present most haphazard 

 and risky manufacture will be doing service to the State. Con- 

 sidering that Cohn only discovered that the ripening process is 

 due to bacteria in 1875, and that Duclaux only published his 

 researches on Tyrothrix in 1878, we can scarcely be surprised 

 that the interval has not been long enough for the isolation and 

 study of the numerous and curious forms, several hundreds of 

 which are now imperfectly known. Nevertheless, there are 

 signs of advance in various directions, and researches into the 

 mysteries of Roquefort, Gorgonzola, Emmenthaler, and other 

 cheeses are being industriously pursued on the continent. Even 

 as I write this comes the news that Freudenreich has discovered 

 the coccus which causes the ripening of Emmenthaler cheese. 

 It is not impossible that the much more definite results obtained 

 by investigations into the manufacture of the vegetable cheeses 

 of China and Japan will aid bacteriologists in their extremely 

 complex task. 



These vegetable cheeses are made by exposing the beans of 

 the leguminous plant Glycine — termed soja-beans — to bacterial 

 fermentations in warm cellars, either after preliminary de- 

 composition by certain mould-fungi, or without this. The pro- 

 cesses vary considerably, and several different kinds of bean- 

 cheeses are made, and known by special names. They all depend 

 on the peculiar decompositions of the tissues of the cotyledons 

 of the soja-bean, which contain 35 to 40 per cent, of proteids 

 and large quantities of fats. The softened beans are first 

 rendered mouldy, and the interpenetrating hyphse render the 

 contents accessible to certain bacteria, which peptonise and 

 otherwise alter them. 



Here, however, I must bring this subject to a close, and time 

 will not permit of more than the mere mention of tlie vinegar 

 fermentation, to which Mr. Adrian Brown has lately contributed 

 valuable knowledge, of the preparation of soy, a brine extract 

 of mouldy and fermented soja-beans, of bread-making, and 

 other equally interesting cases. 



When the idea of parasitism was once rendered definite, as 

 it was by De Bary's work, and the fundamental distinction 

 between a parasite and a saprophyte had been made clear, it 

 soon became evident that some distinction must be made be- 

 tween obligate faailtative pai-asiles and saprophytes respectively ; 

 but when De Bary proposed the adoption of these terms of Van 

 Tieghem's he can hardly have contemplated that they would be 

 abused as they have been, and was clearly alive to the existence 

 of transitions which we now know to be so numerous and so 

 gradual in character that we can no longer define any such 

 physiological groups. 



Twenty years ago Peiiicillium and Mticor would have been 

 regarded as saprophytes of the most obligate type, but we now 

 know that under certain circumstances these fungi can become 

 parasites ; and the border-land between facultative parasites and 

 saprophytes on the one hand, and between the former and true 

 parasites on the other, can no longer be recognised. 



In 1866 the germ of an idea was sown which has taken deep 

 root and extended very widely. De Bary pointed out that in 

 the case of lichens we have either a fungus parasite on an alga, 

 or certain organisms hitherto accepted as algae are merely in- 

 complete forms. In 1868 Schwedendener declared the lichen 

 to be a compound organism. 



In 1879, in his celebrated lecture, De Bary definitely launched 

 the new hypothesis, and brought together the facts which 

 warranted his disturbance of the serenity of those unprepared to 

 accept so startling a new notion as Symbiosis. 



The word itself, in the form " Symbiotismus," is due to 

 Frank, who, in an admirable paper on the biology of the thallus 

 of certain lichens, very clearly set forth the existence of various 

 stages of life in common. 



This paper has been too much overlooked ; but its existence 

 is the more noteworthy from its being in the same number of 

 the " Beitrage zur Biologie" — which we owe to Cohn, the 

 founder of scientific bacteriology — in which Koch's remarkable 

 paper on Anthrax occurs. 



The details of these matters are now principally of historical 

 interest ; we now know that lichens are dual organisms, com- 

 posed of various algse, symbiotic with ascomycetes and even 

 basidiomycetes, and, as Massee has shown, even gastromycetes. 

 The soil contains also bacterio-lichens. The point for our con- 

 sideration is rather that botanists were now awakened to a new 

 biological idea — viz. that a fungus may be in such nicely 

 balanced relationships with the host from which it derives its 

 supplies as to afford some advantage in return, whence we must 



NO. 1455, VOL. 56] 



look upon the limited liability company formed by the two 

 symbionts as a better business concern than either of the plants 

 could establish for itself — a case, in fact, where union is strength. 

 Symbiosis, consequently, is now understood to be of advantage 

 to both the symbionts, and not to one only, as is the case in 

 parasitism, or, to use Vuillemin's term. Antibiosis. 



In 1 84 1 an English botanist, Edwin Lees, discovered 

 the existence of " a hirsuture that appears like a byssoid 

 fungus" on the roots of Monotropa, and observed that the 

 hyphge linked the roots to those of a beech ; he regarded the 

 fungus as conveying nutriment from the latter to the former, 

 and as an essential constituent of the Monotropa. This discovery 

 was published in the now defunct " Phytologist " for December 

 1 84 1, and was unearthed by Oliver and by Dr. Dyer, of Kew. 

 This is apparently the first observation of a mycorhiza yet 

 recorded, and, although the naturalists referred to did not under- 

 stand the full significance of Lees' find, several of them made 

 excellent guesses as to the meaning of the phenomenon. As Dr. 

 Dyer points out, it disposes of Wahrlich's claim that Schleiden 

 (1842) first discovered mycorhiza, as well as of Woronin's con- 

 tention that the priority is due to Kamienski, though the latter 

 (1881-82) probably was the first to clearly indicate that we 

 have here a case of symbiosis, and thus anticipated Frank's 

 generalisation in 1885. 



Kamienski and Frank, followed by numerous other observers, 

 among whom Oliver and Groom are to be mentioned, have now 

 shown that the peculiar type of symbiosis expressed in this 

 intimate union of fungus-hyphte with the living cells of the roots 

 of trees and other plants in soils which abound in vegetable 

 remains — e.g. leaf-mould, moors, &c. — is very common. 



In the humus of forests we find the roots of beeches and other 

 Ctipulifei-cc, willows, pines, and so forth, clothed with a dense 

 mantle of hyphee and swollen into coral-like masses of myco- 

 rhiza ; in similar soils, and in moorlands which abound in the 

 slowly decomposing root-fibres and other vegetable remains so 

 characteristic of these soils, the roots of orchids, heaths, gen- 

 tians, &c., are similarly provided with fungi, the hyphae of which 

 penetrate further into the tissues, and even send haustoria into 

 the living cells, but without injuring them. 



As observations multiplied it became clear that the mycorhiza, 

 or fungus-root, was not to be dismissed as a mere case of roots 

 affected by parasites, but that a symbiotic union, comparable to 

 that of the lichens, exists ; and that we must assume that both 

 the tree and the fungus derive some benefit from the con- 

 nection. 



Pfeffer, in 1877, suggested that the deficiency of root-hairs 

 observed in orchids might be explained by the fungus-hyphte 

 playing the part of these organs, and taking up materials from 

 the soil which they then handed on to the roots. He is quite 

 clear on the subject, and recognises the symbiosis definitely, 

 comparing it with other cases of symbiosis indicated by De Bary. 



Frank stated that, as the results of experiments, seedling 

 forest-trees cannot be grown in sterilised soil, where their roots 

 are prevented from forming mycorhiza, and concluded that the 

 fungus conveys to the roots organic materials, which it obtains 

 by breaking down the leaf-mould and decaying plant-remains, 

 together with water and minerals from the soil, and plays 

 especially the part of a nitrogen-catching apparatus. In return 

 for this important service the root pays a tax to the fungus by 

 sparing it certain of its tissue contents, and no doubt can well 

 afford to do so. 



It appears that the mycorhiza is only formed where humus or 

 vegetable-mould abounds. In sandy soils the roots bear root- 

 hairs, as usual, and it is now clear that, while mycorhiza is a 

 far more general phenomenon than was previously supposed, it 

 is not essential for all the roots, nor even under all circumstances 

 for any of them. 



Probably what really happens is this. Trees and other plants 

 with normal roots and root-hairs, when growing in ordinary soil, 

 can adapt their roots to life in a soil heavily charged with humus 

 only by contracting the symbiotic association with the fungus 

 and paying the tax demanded by the latter in return for its sup- 

 plies and services. If this adaptation is impossible, and no 

 other suitable variation is evolved, such trees cannot grow in 

 such soils. 



In certain cases — e.g. ground orchids, Monotropa, various 

 Ericacea, &c.— it would seem that the plant is unable to grow in 

 other than humus soils, and always forms mycorhiza. 



Much further we cannot at present go, but it is evident that 

 various different grades of symbiosis exist in these mycorhizas. 



