ACTION OF PLANTS ON THE SOIL. 



itself all its carbohydrates and albuminoid compounds cannot remain dormant, 

 but are split up without delay into those simpler compounds of which they were 

 compounded in the summer; and, by the following spring there is nothing more to 

 be seen of any of the pond-weed's stems and leaves. Certainly this is only to such 

 a conspicuous extent true of plants living under water; dead plants buried in earth 

 or exposed to the atmosphere are resolved less rapidly, and under certain circum- 

 stances deposits of organic remains on limited areas are preserved even almost 

 unaltered through boundless ages. 



Let us try to obtain a somewhat closer knowledge of these various degrees of 

 preservation. Thoroughly dried wood, leaves, and fruit, if protected from all but 

 transient moisture, are capable of being preserved unaltered for long periods of time. 

 When wood is exposed in a dry place to the sun, it turns brown, and in the course 

 of years becomes quite black outside, the most superficial layers being regularly 

 carbonized, as may be seen particularly well in the case of woodwork situated 

 under the projecting roofs of old mountain chalets. This wood exhibits no sign of 

 crumbling, mouldering, or rotting. In the dry chambers of old Egyptian graves 

 fruits, foliage, and flowers have been found which were laid by the side of the 

 dead 3000 years ago, and they had not undergone a greater change than if they 

 had been dried but a few days. Even the colours of flowers of the Larkspur, the 

 Safflower, and other plants of the kind, were still apparent, and the separate 

 stamens in Poppy flowers were in a state of complete preservation. Dry ness there- 

 fore may be looked upon par excellence as one of the preventives of the decomposi- 

 tion of organic matter. 



The same result as is secured by dry ness in the cases cited is brought about in 

 the ground of moors by humous acids. The dead plants saturated with these acids 

 are not resolved into carbonic acid, water and ammonia, but preserve their form and 

 weight almost unaltered, and are converted into peat. Above the mass of peat new 

 generations of plants continue to spring up and produce ever fresh organic matter, 

 which, in its turn, becomes peat, and is added to the mass beneath, so that gradually 

 a very deep bed of organic matter may be accumulated in this manner. In the low 

 country lying between East Friesland and the Hummling, from the river Hunte to 

 the marshes on the Dollart, there is a stretch of nearly 3000 sq. kilometers covered 

 with a layer of peat which has an average depth of 10 meters. 



Of minor importance is the preservation of dead plants and parts of plants in 

 snow and ice. The leaves, twigs, and seeds, which are carried by the wind on to 

 the snow-fields of the high mountains, remain there a long time almost without 

 alteration in respect of form or size; they only turn brown under the influence of 

 the intense sunlight, and at last become quite black as though they were carbonized, 

 which, in fact, they are. So also such insects as meet their death on the snow-fields 

 are converted there into a black, cindery mass. Indeed, even all the minutest 

 organic fragments lying on a glacier become carbonized, and this explains the fact 

 that the so-called cryokone, or snow-dust, which we have already had occasion to 

 allude to, has a graphitic appearance. 



