163 



be economically promoted, the farmer and forester may have the 

 control of sources of real wealth not yet dreamt of." 



It follows from what has been said, that if leguminous plants, 

 such as peas, are planted as a crop, they will absorb nitrogen 

 from the air and store it up partly in their leaves, partly in their 

 roots. If, therefore, peas are grown as a crop they should in- 

 crease the total nitrogen in the soil, especially if they be all 

 ploughed in. This has been found to be the case, hence the use 

 of peas for this purpose. 



You will not have failed to notice in what has been said the 

 association of organisms in bringing about certain results. This 

 phenomenon, under the name of symbiosis, is attracting great 

 attention in the scientitic world, and is proving to be of far- 

 reaching importance. In its widest sense the term may be 

 applied to almost any association of living beings whereby im- 

 portant results are brought about ; for instance, the association 

 of the plague bacillus with rats, the bacillus of malarial fever 

 with mosquitos, ikc. In the narrower sense, however, the term 

 is used of the co-operation of two or more associated organisms 

 for their mutual benefit. Professor Marshall Ward, in a paper 

 read before the British Association in 1899, brings out the salient 

 points in recent results on this subject, and to this paper I am 

 chiefly indebted for the facts to be brought under your notice. 



Several instances are now known in which different kinds of 

 bacteria can, when associated, complete processes which no one 

 kind can complete by itself ; witness, for instance, the process of 

 nitrification already referred to. Another remarkable instance 

 is quoted by Winogradsky, who has shown that an anaerobic 

 bacterium, Clostridium pasleurianuin, is able, if supplied with 

 sufficient glucose, and protected from oxygen, to fix atmospheric 

 nitrogen. Now such conditions are not easy to bring about 

 artificially, but when Clostridium pasteurianum is active, it is 

 found to be always working in the meshes of a network of 

 aerobic, that is, of oxygen consuming bacteria, the latter render- 

 ing possible the activity of the former. Similar phenomena have 

 been observed with fungi. The Japanese drink, saki, or rice 

 wine, is made by infecting the steamed rice with a fungus known 

 as Aspergillus oryzcB. This converts the rice starch into sugar, 

 which then undergoes fermentation by the influence of a variety 

 of yeast fungus. So closely is this yeast associated with the 

 Aspergillus that for some time a controversy existed as to whether 

 the former was not really a part of the life history of the latter. 

 It is now recognised, however, that we have here a striking case 

 of symbiosis. 



Every gardener is aware that whereas certain plants, roses, 

 for example, can be transplanted without difficulty, others are 



