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nitrogenous materials from the vegetable mould, and hands some. of 
these substances on to the plant in return for carbonaceous and per- 
haps other organic food-materials supplied by it. In any event, it 1s 
clear that the higher plant derives benefit from this symbiotic associa- 
tion in proportion to that enjoyed by the fungus, and in no case 1s 
this clearer than in that of the Orchids. Bernard has shown that the 
reason horticulturists have such difficulties in getting many orchid 
seeds to germinate is because the young seedling cannot develope un- 
less its root is infested with the proper fungus immediately it emerges 
—a condition not always realisable. The same worker, as also Stahl, 
MacDougal and others, have also extended our knowledge of other 
forms of Mycorhiza of late, and the main facts are no longer in serious 
dispute among botanists. Green plants growing in humus have either 
to compete with the Fungi in the soil for the salts, especially po- 
tassium and phosphorus salts, which these Fungi are so well able to 
collect, or they have to compromise, as it were, with these Fungi and 
offer them something in return for such salts. That seems to be the 
raison détre of Mycorhiza. I find it impossible to avoid asking 
whether these mysterious “ ground” species are not struggling to ob- 
tain their nutriment from very different materials, and under very 
different conditions, and whether the circumstances of their varying 
nutrition do not affect them. 
Obviously, the most satisfactory way of deciding these questions 
would be to do as we do in gardens with higher plants, viz., grow the 
alleged varieties and species side by side and record their behaviour. 
It happens, however, that just this method is peculiarly difficult of 
application to just these particular Fungi—the Hymenomycetes. 
Still, we are making a beginning, and already the labours of Van 
Tieghem, Brefeld, Costantin, Matruchot, Biffen and myself have led 
to results of importance, and shown that we shall gradually learn the 
conditions necessary for successful cultures, and I hope that my en- 
deavours to extend these to parallel cultures may yet lead to success. 
At present, however, the difficulties have appeared almost unsur- 
mountable, for reasons at which there is time only to glimpse just 
now. 
If we ask what are the important features in the nutrition of those 
Hymenomycetes which grow on wood, dead leaves, and on humus, it 
must be admitted that very little is known. Several workers, myself 
among the number, have succeeded in cultivating various species of 
Stereum, Pleurotus, Collybia, etc., from spore to spore, and Brefeld 
especially has brought out a number of interesting facts concerning 
the morphology of such cultures with which, however, we are not here 
concerned. : 
Some of these cultures are relatively easy, as Biffen, working with 
Collybia velutipes in my laboratory, showed, and as my own experience 
with Stereum hirsutum demonstrated. With others, however, the re- 
verse is the case. I will give you two instances. Last autumn I 
started pure cultures of Marasmius androsaceus and of Mycena vul- 
garis, and from the ease with which the spores germinated, anticipated 
