The structure of the mold plant is similar to that of a very small vine, the branches of which are many and are closely massed together. The tiny threads or filaments of mold resemble the vine and its branches. These threads keep sending out new shoots which spread rapidly all over the surface the mold is growing on, and the fruit of the mold plant, which is called spores, is similar to the little berries which grow at the ends of the branches of a vine. These berries are the fruit of the vine; spores are the fruit of the mold plant. Just as the berries contain seeds which reproduce the plant, so the tiny spores contain the seed which will reproduce the mold plant. These spores grow at the end of the mold threads or branches, and when ripe, either fall on the surface directly beneath, or are carried away by a breath of air and move along with the dust. The spores of the mold plant will remain alive for months in a dry state, floating in the air, or if the air be very still, falling to the surface. The air everywhere is full of them, and as soon as they light upon a moist surface, such as tomato juice, for example, which contains nourishment for them, they begin to send out shoots of mold threads and reproduce another mold plant. [Illustration: Fig. 4.—Mold filament from catsup. (×150.) ] Mold grows most rapidly upon a warm surface, preferably about the temperature of the human body. It will not grow on a surface which is at freezing temperature, or on a very hot surface. Under these extremes of temperature it is unable to multiply itself. Boiling kills the mold plant, and continued boiling of 15 minutes or more also kills the seeds or spores of practically all species. That is one reason why it is desirable to bring peeled tomatoes or tomato juice to a boil as soon as possible—so that the mold and mold spores which are always on these surfaces will be killed before they have an opportunity to grow. There are many different species or varieties of mold plants which thrive on tomatoes and tomato pulp, but they are all very similar; they reproduce themselves in exactly the same way, and they are all arrested in their growth by extremes of temperature, and are killed by continued boiling. It should not be thought, however, that boiling for a very few minutes will kill all mold spores, as they have a tough surface which has considerable resistance to heat. I have seen 5–gal. pulp packed which was only given a very short boil on account of low steam pressure, and molds grew in the sealed cans after packing to such an extent that the pulp all had to be thrown away. It is safe to assume, however, that a 15–minute boil will kill mold spores and prevent the growth of molds in the cans after they are sealed, providing, of course, that the pulp is filled hot into cans which are clean and almost sterile. Bacteria