(1) The ⑥ embryo of kidney bean seed consists of four parts: ② embryo, ③ radicle, ④ cotyledon and ① hypocotyl. Embryo is the main part of seed, and the main function of cotyledon is to store nutrients.

(2) In the process of seed germination, radicle grows fastest, develops into root, embryo develops into stem and leaf, hypocotyl develops into a part connecting stem and root, and embryo develops into a new plant larva.

(3) In order to germinate, seeds must meet certain external conditions such as moisture, suitable temperature and sufficient air.

So the answer is: (1) hypocotyl; Germ; Radicle; Cotyledon; Embryo; Store nutrition

(2) the connecting part of stem and root; Stems and leaves; Root; Larvae of new plants

(3) Suitable temperature; A certain amount of moisture; Plenty of air