The point of developing brassicas without using a bit of ready-mix (8)

I believe the answer is:

abscissa

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But I can't explain it at all! Could you help me understand?

(Other definitions for abscissa that I've seen before include "Intercept" , "X co-ordinate" , "quantity on graph" , "X-coordinate on a graph" .)

I've seen this clue in The Hindu.

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