240 'riili/i/sl.rlli .\iiinnil MrrliiKJ 



It is \\(ii-tli wliilc to (l('\()tc ;i few \\()i-(ls lo Liascous |)r()(liict> 

 nf (lcc<.iii|i(.si|i()ii (illici- tllJin riirlinii diiixidc. S<i loliu- as the 

 lidttniii WMtcr (•(tiilniiis ;in aliiimlniicr n\ dxyncn no otiicr ,l;';i- tliai* 

 cni'licii ilioxidc is produced in apprccinlilc (|iiiiiil it ics. liiil a> 

 the (!.\\\m'ii liccoiiics L;i'c;illy f»Mluc('(| oi' wliollv dis;i ppcai's. dc- 

 coiiiposilion coDtimics in new rorni>. ;ind uiidrr tlicsi' (•ond'lion> 

 (d' ;ii),ifi-oliic rci-nicnt;ition other i^nses ni;iy lie dexcloped in con- 

 sidernlde nnionnt. It is ii|)|);ireiit ly tiMie that cai'hon monoxide 

 may he pi'eseiu ill the h)wei' watei' of hd<t's in appreciahle ()uan- 

 tities. and it is certain that mai'sh j^as 's dpveloped in hirLic \()l- 

 nnaes in hikes where the anioniit of fermentalde material is u'lvat 

 and where the oxyii'en (lissa|)ears fi-oiii the lowei' water e;irly in 

 tlie serison. Tliese gases lirst appeal' near tlie hottoin. where de- 

 eoiiijiositioii is goiiiii' on most aeti\('ly and where oxygen lirst 

 (lisap])ears. In many lakes they are found onlv in small (jiiaiiti- 

 ties and close to the liottoiii. hut in jiroportion as the amount oF 

 deeom]iosal)le niatti'r increases, tliey are found at coiwiderahle 

 distances from tlie hottoin. and in certain lakes all of the water 

 helow the tliermocline may contain marsh .u'as in appreciahle 

 qnantities, often hecomino- \-ery ^reat as the hottoin is ap- 

 proached. These gases do not seem to Inive any very detiiiite uii- 

 favorahle effect on the life of the lak-e. Diffusion is so slow that 

 they do not reach the up|)er water and ex])eriments indicate that 

 their ])resence in the lower water adds little, or nothing, to the 

 unfavorahle conditions hrought aliout l)y the aljsenct' of oxygen. 

 ■ It should he noted that these ])roeesses involve a loss of nie- 

 terial f(n' ])lant food. Carhon dioxide. ])r(Mluced hy aerohie de- 

 composition, is availahle for plant food in the lake. or. if not 

 there, then elsewh.ere as jiart of the general stock of that gas 'ii 

 tlie atmosphere. I>iit marsh gas has no such relation to plants 

 and all suhstances converted into it are lost to the eyek' of life. 

 Its production means just so much reduction of the food supply 

 of the lake. The same may he said of the carbonized, peal-like 

 substances prodnced from the partial decomposition of i>lants 

 under water. So long as these remain under water, they are 

 jiractically withdrawn from the food supply. Against all these 

 influences which tend to diminish the stock of food for its in- 

 hahitants. the lake is t-onteiiding. hut with imperfect means and 

 only jiartial success. 



