“There, Charles,” said the grandmother, “wouldn’t a vest pocketful of those bugs or germs be a big enough dose for one acre?”

“Well, but they’re not a fertilizer, Mother,” said Mr. West, “and besides Mr. Johnston says it is better to use the infected sweet clover soil and there is no need of paying $2 an acre for something we knew nothing about, and especially on land that is not worth more than $2 an acre.”

“I don’t care what it’s worth,” she replied, “some of it cost your grandfather $68 an acre, and it will never be sold for any $2, while I have any say so about it.”

They waited for Percy to proceed.

“The individual bacteria are very short-lived,” he continued, “and products of decay soon begin to accumulate in the tubercles.  These products contain, in combined form, nitrogen which the bacteria have taken from the air, and in this form it is taken from the tubercles and absorbed through the roots into the host plant and thus serves as a source of nitrogen for all of the agricultural legumes.

“It should be kept in mind, of course, that the red clover has one kind of nitrogen-fixing bacteria, that the cowpea has a different kind, and that the soy bean bacteria are still different, while a fourth kind lives on the roots of alfalfa and sweet clover.”

“How much infected sweet clover soil would I need to inoculate an acre of land for alfalfa?” asked Mr. West.

“If the soil is thoroughly infected, a hundred pounds to the acre will do very well if applied at the same time the alfalfa seed is sown and immediately harrowed in with the seed.  If allowed to lie for several hours or days exposed to the sunshine after being spread over the land the bacteria will be destroyed, for like most bacteria, such as those which lurk in milk pails to sour the milk, they are killed by the sunshine.”

" That’s right,” said the grandmother.  “That’s the way to sterilize milk pails and pans and crocks.  I like crocks better than pans.  They don’t have any sort of joints to dig out.”

“Of course,” continued Percy, “a wagon load of infected soil will make a more perfect inoculation than a hundred pounds, and where it costs nothing but the hauling it is well to use a liberal amount.”

“How deep should it be taken?” asked Mr. West.

“About the same depth as you would plow.  The tubercles are mostly within six or eight inches of the surface.  The bacteria depend upon the nitrogen of the air and this must enter the surface soil.  Sometimes in wet weather the tubercles can be found almost at the surface of the ground, and when the ground cracks one can often find tubercles sticking out in the cracks an inch or two beneath the surface but protected from direct sunshine.