plant foods. The alfalfa root or rootlet becomes enlarged at the
point attacked by the bacteria, and a sort of wart or tubercle is
formed which resembles a tiny potato, as large as clover seed on
clover or alfalfa, and, singularly, about as large as peas on
cowpeas or soy beans. On plants that are sparsely infected, these
tubercles develop to a large size and often in clusters. While the
bacteria themselves are extremely small and can be seen only by the
aid of a powerful microscope, the tubercles in which they live are
easily seen, and they are sufficient to enable us to know whether
the plants are infected."

"I wish you would tell me the difference between the words
inoculated and infected," said Adelaide.

"Inoculated is used in the active sense and infected in the
passive," said Percy. "Thus the red clover growing in the field is
infected if there are tubercles on its roots, although it may never
have been inoculated; and we inoculate alfalfa because it would not
be likely to become infected without direct inoculation."

"Under favorable conditions," continued Percy, "these bacteria
multiply with tremendous rapidity, somewhat as the germs of small
pox or yellow fever multiply if allowed to do so. A single tubercle
may contain a million germs which if distributed uniformly over an
acre would furnish more than twenty bacteria for every square foot."

"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