Hotifern, such us A S J ~U ) I C / ~I ~U , niiiy linvc produced
it niore hcitvily grazed crop in April nntl i\Iiiy, eveu under this fnster rntc of division, t,liriii enrlier in the pear.
1\Tonc the ICSY, these considerations suggest tluit n knowledge of the true rntc of silicon depletion, i.e., fall in coiiccntrntiol~s of dissolved silicon in the free wnter plus return of silicon froin tlic bottom* nnd of vnrintions in the wiglit of silicon incorporntcd in the stmi&ng crop of clintonis over the period, will cniiblc p nnd nuiirtions of 11 to IJC conii)uted for thnt period. It sIioriId tIiris be possibIc to: nssess niortnlity rntes nnd nrrirc nt truc gross pcoductiLn iu tiliturn1 plmiktonic diiitoin poptilntious by relutively sirnple incutis.
Thc 1ios:'ibility tlint tlrc rntc of rcturu of silicoti from Lottom deposits cnn be iis high its 2.0 mg. Sill. per neck rniaes 11 point of sonic iniportt~ncc. W e r e the nren of shnllows in a deep, eutxopllic lnkc is estcnsive, it must be I)resunied tliut silicon will be rcturnctl to tlic wnter stnndiug nbovc these shnlloas. Oflsliorc winds will sI)read this water over deeper wens, the result hing to Tlius, froin tlic poiut of view of silicou relileuisl~inciit (or tliiit of other suI)stnnccs returuing to circulation from the I U I I ~) the epilimnion ~horild not be regarded ns coniplctely cut off from tfic bottom during tiiiics of tliernid stmtificntion. The nniount by which the silicon contcnt could be riiiscd is unlikely to be grcnt nntl will be governed by the rntio of the iiren of slinllo\vs to the total iircn of the lake nnd by tlie niiturc of the bottom niuds.
Certain 0 t h fiictors will hare to be taken into consideration before the coefficient of correlirtiou of silicon depletion and silicon incoq~orntio~i sllould be coinputed. The first of these is thnt the weight of silicon per cell ~nny decrensc ns n pol~t~lr~tion of diutoins ]ins becii longer cstnblislicd, n suggcstiou niudc by Eiiiselc : i d Grim (Ioe. cit., 11. 563). The following results liuvc been computed froin data given by these nuthors.
. rnise the silicon contcut of the epilininioii. TA111.C 11' nCaI1 WCiglrf of silicon per cell of Frngilnrin crotoncnsis OIL dafW shown, logrlhertoi/h tiumber ofeellaper ml. anfhe aaiae datw so. of Si wt cclls pcr ccll lwr nil. trig.-* Si Dntc a I U X I 31ay ID . , 250 80 20,000 llnv 30 .. 300 70 21,000 J u h 2 . . 360 ao 21,000 J i m 10 .. 300 70