DEOUGHT AND GAEDENING. 



213 



fully understood. It has been shown that the fungus of the mycor- 

 rhiza of some peat plants is a nitrogen-combiner and is able to tap 

 the atmosphere as a source of nitrogen directly, and to bring the 

 nitrogen into combination — a function only comparatively recently dis- 

 covered as belonging to a 'few bacteria, and supposed to be a function 

 of them alone. And therefore these peat plants, living in an environ- 

 ment whence nitrogen in the form of nitrate usually taken in by roots 

 is not abundant, are able directly to obtain nitrogenous compounds 

 manufactured by the fungus. 



And here I may interpolate. The determination that this power 

 belongs to higher fungi leads us to a much broader view of the role 

 of fungi in Nature. Of their destructive power in living organisms, 

 of their work in restoring to the service of life the nitrogen locked 

 up and no longer of immediate purpose in the dead bodies of plants 

 and animals, we have long known. But now the trend of evidence 

 is towards the establishment of their position as circulators of 

 nitrogen, not merely through decomposition, but also by bringing 

 primarily from the store of the air fresh supplies for the service of 

 living things. To the nitrogen of the air they would appear to stand 

 in the relation which the green plant has to the carbon dioxide. A 

 wonderful filling up this of the picture of the inter-dependence of 

 living things. 



Another feature in peat plants in their relation to' physiological 

 drought is most characteristic — that of the development of an acid 

 mucilage. That the cell membrane of root-hairs' may become 

 mucilaginous, and thereby offer the plant means by which to cement 

 its absorbing cells to the particles of soil from which they take in water, 

 is a commonplace of botany, but the condition in the peat plants 

 to which I refer appears more precisely determined. A distinctively 

 marked mucilage-forming layer appears behind the root-tip, and 

 through it the whole root becomes bathed in mucilage formed from it 

 (see fig. 71), much in the same way as in the well-known cases of desert 

 grasses and other plants, where the mucilage sheath becomes the 

 cement of the sand tunic covering the roots. That this mucilage has 

 something to do in connexion with water-intake is a natural conclu- 

 sion, and it is noteworthy that it does not melt away readily in the 

 water around it, but its exact relationship to water-intake and to the 

 soil environment is not yet clear. Its early appearance and copious- 

 ness must preserve in the developing root an envelope holding moisture, 

 which we m^ay interpret as connected with the physiological drought. 

 In many peat plants there would seem to be also some correlation 

 between this and a late development of the water-carrying system 

 within the root. The manner, too, in which the mucilage spreads out 

 from the root over substances placed in contact tempts a suggestion of 

 a still more important relationship on the part of the root. Certain 

 IS it that such roots laid on blocks of egg albumen groove them in much 

 the same fashioa as roots will impress their form on the surface of 

 marble. In the Ericaceae the mucilage is present without any root- 



