846 REPORT — 1897. 



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 

 between obligate facultative 2}arasites and sajvophytes respectively ; but when 

 De Bary proposed the adoption of these terms of Van Tieg hem'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 Penicillium and Mucor 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 incomplete forms. In 1868 Schwedendener declared the lichen to be 

 a compound organism. 



In 1879, in his celebrated lecture, De Bary definitely launched the new hypo- 

 thesis, 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 note- 

 worthy from its being in the same number of the ' Beitrage zur Biologie ' — which 

 we owe to Cohu, the founder of scientific bacteriology — in which Koch's remark- 

 able paper on Anthrax occurs. 



The details of these matters are now principally of historical interest ; we now 

 know that lichens are dual organisms, composed of various alg», 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 relati3nships with the host 

 from which it derives its supplies as to afford some advantage in return, whence 

 we must look upon the limited liability company formed by the two sj'mbionts 

 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 under- 

 stood to be of advantage to both the symbionts, and not to one only, as is the case 

 in parasitism, or, to use VuiUemin's term. Antibiosis. 



In 1841 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 hyphse 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 1841, 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 understand the full significance of 

 Lees' find, several of them made excellent guesses as to the meaning of the pheno- 

 menon. As Dr. Dyer points out, it disposes of Wahrlich'a claim that Schleiden 

 (1842) first discovered mycorhiza, as well as of Woronin's contention 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-hyphas with the living cells of 

 the roots of trees and other plants in soils which abound in vegetable remains — 

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



