103 



Since more water is drawn away from the ducts than can be replaced 

 instantly, a space partially filled with air appears in these ducts causing a 

 negative pressure (suction) which is so much the greater the less the amount 

 of air present at tlie beginning or slowly diffused through the membranes, for 

 so much the more must the originally small volume of air be distended to fill 

 out the hollow space which is always becoming greater. In the night, when 

 the evaporation is arrested or very much repressed, the ducts of the trunk 

 again suck up great amounts of water, in fact, this suction is often increased 

 by the pressure proceeding from the roots which can press so much water into 

 the ducts that a great part passes through the membranes into the surround- 

 ing cells and intra-cellular spaces. If this liquid drawn up from the root body 

 or pressed up by it is healthy, a considerable infiltration into the intercellular 

 spaces will take place without disadvantage to the body, as has been 

 shown by Moll\ If, however, the water mass is already laden with the 

 products of fermentation from the putrefying root tips, we see that these 

 poisonous substances get into the especiaUy sensitive sapwood and bark and 

 thus the dying back easily spreads. 



Trees planted too deep, however, usually die only in heavy soil per- 

 manently loaded with water. In light soils they suffer but do not die. If the 

 heavy soil with its water burden surrounds the base of the trunk and pre- 

 A'ents intercellular ventilation by means of the lenticels, alcoholic fermenta- 

 tion and the formation of acetic acid must naturally appear in the bark cells 

 and lead to a dying back which is continued radially to the cambial zone and 

 the young sapwood which is especially active in conducting water. 



Thus there remains from year to year a cylinder of heartwood in the 

 middle of the trunk which is always becoming smaller and smaller and which 

 usually has to meet the water need of the aerial part. The heartwood which 

 is poor in water, however, is less suited for conducting it and the dead tis- 

 sues of the wood, which at any rate can still conduct water mechanically, 

 Vvill not be able with their help to meet the need of water in the crown. Con- 

 sequently, the tree uhimately wilts or fails to put out buds in spring. 



The fact that the non-parasitic processes of decomposition in the buried 

 end of the trunk cease near the upper surface of the soil leads to the theory 

 that processes of decomposition are not able to attack healthy plant cells but 

 only those weakened and functionally abnormal. Such weakening is actually 

 present. It was mentioned at the beginning that cells full of life and rich in 

 content, when shut away from the oxygen of the air, begin at once to de- 

 velop alcohol through the activity of fermentation (alcoholases) which was 

 not present previously and which disappears again if the plant regains its 

 atmospheric air. It has been proved further that the plant, in the absence of 

 oxygen, continues for some time to eliminate carbon dioxid in considerable 

 quantities (respires intra-molecularly) but that these amounts of carbon 



1 Untersuchungen iiber Tropfenausscheidung und Infektion, 18S0 p. -8 Sep. 

 aus Verslag en Mededeeling d. Koninkligke Akad. Amsterdama, cit. in Pfeffer, 

 Pflanzenphysiologie, 1881, I, p. 159. 



