134 TlMEHRI. 
plants concerned. LlEBIG, whilst agreeing with Davy 
that gypsum acted as a plant food per se, attributed its 
action chiefly to its power of absorbing and fixing the 
carbonate of ammonium, that SAUSSURE about that time 
had proved to be a constituent of air, and particularly 
that portion of it carried from the air to the soil by rain. 
In fact, LlEBIG regarded the application of gypsum as 
equivalent to manuring the soil with an ammoniacal salt. 
Both theories were ably criticised by BOUSSINGAULT, 
who, indeed, seems to have had the best of the argument. 
He found from the analysis of ashes of clover that had 
and had not been manured with gypsum, that in each 
case the quantity of lime absorbed by the plant was out 
of all proportion to the sulphuric acid ; so that the 
mineral could not have been absorbed in its entirety. As to 
LlEBIG'S ammonia theory, BOUSSINGAULT showed that 
to double an ordinary crop of clover, which a dressing of 
gypsum is well known to do, the rain falling during the 
growth of the plant, must have contained not less than 
tt,^oo of its weight of carbonate of ammonia, or about 
four grains per gallon, whereas rain water certainly did 
not contain anything like such an amount. He further 
pointed out that if gypsum acted by supplying ammonia, 
it should benefit not only leguminous crops, but also 
those known to be increased by ammoniacal salts, which 
was not found to be the case. 
BOUSSINGAULT, himself, considered that gypsum acted 
merely by supplying lime to the crops, but was in his 
turn confuted by Way, who pointed out that the appli- 
cation of gypsum doubles the yield of red clover, an 
average crop (per acre) of which only contains 55 lbs. of 
lime ; of white clover, containing 45 lbs. of lime ; of 
