i8;6.] 
Infusorial Earth and its Uses , 
343 
successive years the proper amount of silica in assimilable 
form for the plant, inasmuch as the liberation of this sub- 
stance by the chemical decomposition of the mineral matters 
of the soil containing it, goes on so slowly as to render 
doubtful the production in many years of the amount re- 
quired for a single crop. In proof of this assertion they 
refer to the great reduction in the yield of the wheat crop, 
since farmers began years ago to sell the straw of the crop 
that formerly was returned to the soil. For this, and other 
reasons less obvious, their attention was attracted to the 
importance of incorporating silica into commercial fertilisers 
- — one difficulty remained to be overcome, namely, the dis- 
covery of a form of the silica — which should be assimilable 
by the plant. This they claim to have found in the infuso- 
rial earth, — in which the silica is in an inconceivably minute 
state of division, — the result of their consideration being 
the production of a so-called “ silicated superphosphate of 
lime,” a superphosphate with which the infusorial earth is 
intimately incorporated. The argument urging the im- 
portance of an abundant supply of silicic acid in available 
form, as an absolute necessity for the proper nutrition of 
cereals, is not disputed ; and the manufacturers, to demon- 
strate the availability of the silica in the form in which they 
employ it, have actually succeeded in proving beyond 
question the highly interesting and novel faCt that the very 
minute skeletons or shells of which the infusorial earth is 
mainly composed are carried up as such into the body of the 
plant itself. Upon this point the following gleanings from 
an investigation conducted by Prof. P. B. Wilson will be 
read with interest : — 
This chemist subjected to a microscopical examination 
the straw from the wheat-fields of Col. J. B. Kunkel, of 
Frederick County, Maryland, which had been fertilised by 
the silicated phosphate, his purpose being to make “ a more 
complete investigation into the siliceous structure of the 
stalk, in determining whether the Infusoria passed direCtly 
as such into the sap-cells, to be carried forward by capillary 
force, and to finally assume their functions, — the formation 
of the epidermal shield for giving strength to the straw, to 
withstand the destructive force of high winds and beating 
rains, as well as a protection against the attacks of 
parasites.” 
“ In making these investigations thorough precautions 
were observed, to cleanse the straw from all accidental im- 
purities by washing and gentle friction, not sufficient, how- 
ever, to destroy the epidermis. The organic matter was 
