Recently I have discovered that if you remove the rose achenes from the hip, then saok them for a couple of days to remove all impurities and bits of hip, then air dry them for several weeks until the achenes are stony hard, then it is much easier to do the achene extractions. Extractions done on freshly collected achenes from a hip versus extraction done a few weeks later on the remaining stone dried achenes from the same hip have proven infinitely much more difficult for me, by comparison.
Part of this ease is to do with the easier handling of a dry seed in your hands (better purchase, less slipping), but also the blade of the box cutter cuts with greater efficiency and less need to recut/force the blade, as the dehydrated achene offers less elastic recoil force to the action of the blade. A bit like how it is easier to slice through a banana than a sponge (ok this is an exaggeration, but you get the point?!!). This means less pushing action when cutting, less re-slicing, and so less potential damage to the seed underneath…and so it is also much FASTER.
Only extra sharp previously unused box cutter blades are to be used for best cutting, there is risk of injury, I cannot accept responsibility for this…be careful or just don’t attempt this if you are clumsy! Also it is best to keep others well away from your operating field, and wear protective eyeware, as occasionally even in the best of hands, seed flies in your face or around the place…(this happens less as you gain experience…LOL).
Another fantastic advantage to drying is that the seed within the achene has also dehydrated and shrunk in volume…but since the achene volume has not shrunk anywhere near the same amount, an air pocket develops around the seed…the drier the seed the more it’s potential volume is replaced by air…This is an insurance policy because the box cutter blade sometimes slices into an air pocket where otherwise it would have struck seed if the seed were fully hydrated. So there is more room to negotiate the slicing without injuring the seed…very cool :0)
Dry achenes with this air pocket within them have also led me to propose something else in relation to why some viable achenes float…
Some achenes have dryer seed than others, for whatever physical reason (eg. extra leaky sutures, or more leaky achene shell)…the drying shrinking seed within such achenes has air replacing its volume as it shrinks. The more dehydrated and shrunk the seed becomes inside the achene, the more volume of air exists to replace the seed volume. At some point of this seed dehydration phenomenon, the buoyancy forces of the water around the achene become greater than the sinking forces as the achene becomes less and less dense…and flotation results.
So NEVER throw out achenes that float!!! They float because there is air in them…some are just achenes with dry viable seed and air pockets, while others are 100% air filled (contain no seed).
Oh, and by the way, if placed in a glass of water the very dehydrated seeds/embryos spring to life very very fast. Nature has it all worked out!