Generally we know that in hydra every part of it comes and grow into individuals but how into a complete hydra ,what is the thing that makes a half part into a full?

A type of reproduction in which a single cell splits into equal parts and each part grows into a complete individual:

What part of a metre is got by dividing 1 metre into 15 equal parts? To get this, into how many equal parts should we divide every metre?

What do we call the part of seed that grows into shoot upon germination?