Maasros chapter 1, mishnah 3. This mishnah is a direct continuation of the previous one: it lists various kinds of produce and establishes when each of them reaches the "season of tithing" - the threshold of edibility from which point on the fruit can actually be tithed, and the tithing takes effect.
The signs of ripening in the various fruits:
"Hecharuvin - mishe'yinakedu" - carobs, once they become spotted. "Nekudim" comes from the word for dots. The carob begins its development green, looking like a pea pod. Later it darkens until it looks almost black, though it is really a deep brown. From the moment those small dark dots appear on the pods, the carob has reached the season of tithing.
"Uvechol hashechorim - mishe'yinakedu" - and so too with every kind of dark colored food: from the moment the dark spots begin to appear on them, they have reached the season of tithing.
"Ha'agasim" - pears; "krustemelin" - which ArtScroll renders as golden nut apples; "haparishim" - quinces; "ve'uzradim" - crustumenian pears. All of these are species that fall somewhere between an apple and a pear - kinds of apples or fruits resembling them. For all of them the measure is set at "mishe'yikarchu", from the word for bald: these fruits are covered at first with a fine down, which later falls off them. Once the down has fallen off and they have become, as it were, bald, they have reached the season of tithing.
"Uvechol halevanim - mishe'yikarchu" - the same applies to every kind of light colored fruit: once they become bald, that is, once the fuzz falls off them, they are considered to have reached the season of tithing.
"Hatiltan - mishe'yitzmach" - fenugreek, once it can sprout. Tiltan is fenugreek, which was already mentioned in the order of Taharos. It is known as "chilbah" among Sephardic and Yemenite communities, and it is also used in Indian cooking. Its measure: from the moment its seeds are fit to sprout. This is tested by placing the seeds in water - if they do not float, but rather most of the seed sinks below the surface, that is a sign that it is fit to sprout, and with that it has reached the season of tithing.
"Hatevuah vehazeisim - mishe'yachnisu shelish":
These two species are especially important, since they are true staple foods. "Tevuah" is grain, and "zeisim" are olives in the plain sense. Their measure is set at bringing in a third: once they have brought in a third, they become subject to the season of tithing.
There are two approaches to explaining this, and both are cited in the Bartenura:
That they have grown to a third of their full size - an explanation that is somewhat difficult to understand, certainly when it comes to grain.
That if they were processed at this stage, one would obtain a third of the normal yield produced at full ripeness. This is readily understood with olives: if they were pressed at full ripeness they would yield three liters per container, whereas now they are ripe only to the point that pressing them would produce a single liter - a third of the usual amount. At this stage they have reached the season of tithing, and a similar calculation applies to grain as well.
In summary: in this mishnah we learned the signs of ripening that determine the season of tithing for each and every species: the dark spots on carobs and on all dark colored foods; the falling off of the down on pears, krustemelin, quinces, uzradim and all light colored fruits; the capacity to sprout in fenugreek, tested by whether the seed sinks in water; and the bringing in of a third for grain and olives - whether that means a third of their size or a third of their yield.