Mishnah Uktzin 2:9: Regarding a zucchini which one planted in a pot and it grew and emerged out of the pot [and onto the earth], it is pure [and cannot be rendered impure]. Rabbi Shimon says: [regarding the part of the plant still within the pot,] what is in its nature that it be considered pure? Rather, that which is [or can be rendered] impure [remains] in its impurity, and that which is pure [i.e. that which is outside of the pot] may be eaten.

קִשּׁוּת שֶׁנְּטָעָהּ בְּעָצִיץ וְהִגְדִּילָה וְיָצְאָה חוּץ לֶעָצִיץ, טְהוֹרָה. אָמַר רַבִּי שִׁמְעוֹן, מַה טִּיבָהּ לִטָּהֵר. אֶלָּא הַטָּמֵא בְּטֻמְאָתוֹ, וְהַטָּהוֹר יֵאָכֵל:

Mishnah Uktzin 2:10: Vessels made of dung or of earth through which the roots can emerge outward do not prime the seeds [inside them to be susceptible to susceptible to being rendered impure]. A perforated pot does not prime the seeds [inside it to be susceptible to being rendered impure]. But that which is not perforated does prime the seeds. What is the measure for a perforation? That through which a small root can emerge. If one filled it to its brim with dust, it is thereby like as a tray without a rim [which cannot be rendered impure, as it is no longer a vessel].

כְּלֵי גְלָלִים וּכְלֵי אֲדָמָה, שֶׁהַשָּׁרָשִׁים יְכוֹלִין לָצֵאת בָּהֶן, אֵינָם מַכְשִׁירִים אֶת הַזְּרָעִים. עָצִיץ נָקוּב אֵינוֹ מַכְשִׁיר אֶת הַזְּרָעִים. וְשֶׁאֵינוֹ נָקוּב, מַכְשִׁיר אֶת הַזְּרָעִים. כַּמָּה הוּא שִׁעוּרוֹ שֶׁל נֶקֶב, כְּדֵי שֶׁיֵּצֵא בוֹ שֹׁרֶשׁ קָטָן. מִלְאָהוּ עָפָר עַד שְׂפָתוֹ, הֲרֵי הוּא כְטַבְלָא שֶׁאֵין לָהּ לִזְבֵּז: