The Gemara derives from the word ulekachtem, and you shall take, that the four species are essential to each other, i.e. that one must have all four species available when he is prepared to fulfill the mitzvah.
It is noteworthy that the Gemara derives this ruling from the word ulekachtem. The sefarim write that the festival of Sukkos is corresponding to Yaakov, regarding whom it is said and Yaakov journeyed to Sukkos. The Medrash states that on Rosh Hashanah the Jews and the gentiles enter into judgment, and it is not discernable who the victor is until the Jews exit from judgment waving the lulav on Sukkos. It is said regarding the Yom Kippur service, the he-goat will bear upon itself all their iniquities, and the Medrash states that the word for their iniquities is avonosam, which is an acrostic for the words avonos tam, the sins of Yaakov, who is referred to as tam, the perfect one. Thus, Yaakov is victorious on Yom Kippur when the he-goat, symbolizing Esav, carries away Yaakov’s sins, and this victory is reflected in the Jewish People waving the lulav on Sukkos. The statement of the Gemara here is thus complemented by the statement of the Medrashim that the sins of thetam are removed and Yaakov is then able to perform a lekicha tama, a perfect taking of the lulav.