Sorry: replying in English 'cos I'm on my 3rd glass of wine...
From the end of p13 and p14, I'm not 100% sure how στάχυ is being used. But σπάδικας is correctly being used for the
inflorescence / ταξιανθία. As suggested by '-flor- and '-ανθ-', this only refers to the 'flowering' stage (they're not true flowers, but let's keep things simple).
The stage which can have 'seeds of varying colours' is no longer an inflorescence/ανθιφορία: it's an infructescence (
http://en.wikipedia.org/wiki/Infructescence ).
Since σπάδικας and θύσανος both refer to ανθιφορίες I don't think they can be used here.
«Θύσανος» seems particularly wrong, because there is no way I would describe a female corn ear (inflorescence or infructescence) as νηματοειδής.
PS - I haven't read past page 14, but if the other 91 pages clearly use σπάδικας to mean the harvestable ear (rather than the inflorescence which has the potential to become a harvestable ear) then I would suggest - however arrogant it may sound! - that the authors have used the terminology incorrectly.