•^•5S 



'rinrti/sl.rlli Ainuuil Mrrlnnj 



lliis process, is ni'owiiiii- ixkuti' iliii'ini:- llic siiiiinicr in llic iiia- 

 ici'inls (in which |>hinls I'ccd. holh pisr.uis niid other. 'These are 

 I'oi' the time locked ii|) in the jowei' watei' and so withdraw ii I'l'oni 

 the cireiihit ion of life. In the autumn, as the hd<e cools and 

 the thickness (d' th(^ circndat in.i:' sti'alum increases, these matters 

 hecome ;i\aihd)le so far as they lie in the upper part of the cooler 

 watei-. and when the lake has hecome uniform in temperatui'e to 

 the hottom, and the watei' is tuimed oxer h\- the wind, the whole 

 (d' this accumulated stock is availahle foi- the pui-po>e> of plant 

 ,-i-owtli. This may he one (d' the reasons loi- the ahundant 

 -I'owih of al,-ae. whi(di ta.kes place in the autumn. I'.ut whMe 

 the non-i;aseous product> ol' decomposition may he wholly util- 

 i/,((l in the lake, the carhon dioxid.' is hardiv lik.dv io liu.l full 

 use. When it once lunomes distrihuted throu-li the water and 

 new portions of the wati r are ludiii:- continually e\po>e<| to the 

 ;i;r. considerahli' (pnintities must escape dni-im:- the houi's when 

 ])lants are unahle to a\ail themselves of it. 



'iduis the i-udimentai'y chai'actei' of the circulatoi-y apjiai'atns 

 of the lake forms an insupei-ahle ohsta(de to the hest utilization 

 of their food snpi)ly. !t is thei'idore easy to see whv life is re 

 lativ(dy so al)undant in lar,u'e and shallow lakes, in which the 

 circulatinii- methods have a maximum etticieiu-y. 'IMie fact that 

 they are shallow ]ierniits a lar^'ei' Lii'owth of life, since not only 

 is the water availahle hut phints in larux' (piantitics ma\- >:row 

 from the hottom. But of e\'eu UKU'e impoilance than thi- re- 

 lation is the fad that since the entire mass of water i,- kept 'n 

 circulation hy tlie wind, all of the pi-oducts (d' decomposition 

 are immediaicdv availahle for use and the lih' cycdes (d' the 

 plants ma\- uo on as rapidly as their rhythm (d' urowth wdl 

 permit. The cai'hon dioxide and othei' produ<-ts of decomposi- 

 tion, instead of heinu- locked up in the deeper watei' and set free 

 only dui'iui:- that season whicdi is less fa\()rahle for :ii-owtli. are 

 utilized innnediately and ai'c employed o\ei- and o\ci' ai;ain 

 thi'o'u.uh the warmei' season as the cycles of life and death of the 

 indi\idual plants recur. It is plain that lake> w ho>e mai'.^in is 

 wide ami shallow, thou-h the mi<ldle may lie deep, must stand 

 next to the shallow lake in ellicieucy of unmans (d' t I'anspoi'tat ion. 

 Mu(di ,i:-rowtli take- place 'n shallow waters. mu(d) decomposition 



o-oes on thei'c. and little (d' tli 



atter siuKs ii 



vp 



