There have been several postings regarding exogenous seeds but I don’t see a diffinitive answer as to what, if anything, should be done with them. I have several varieties that I am excited to see has produced many hips, but it appears that most, if not all the seeds are on the outside of the hips hips. I can always put on some parchment paper caps like Judith has suggested but I am wondering if it is worth my time.
Has anyone determined if the germination rate of exogenous seeds is different than those that are grown inside the hip? Sunburning, and drying out were some issues that have been raised and I am wondering if anyone has noticed any of this? Also, what about color changing in the hip? I am dating all my hips so that I give them 120 days to mature, but if I was waiting for the color of the hip to change, I think I might miss out on these ones.
Also, has causation/predictability of exogenous seeds been determined? Perhaps one method of predicting exogenous seeds may have something to do with the shape/structure of the recepticle of the bloom in addition to the number and size of the seed. I have noticed that with many of my seed parents with recepticles that are flat, as opposed to being cup shaped, exogenous seeds are common. I am interested to see if others have also noticed the shape differences in those that produce exogenous seeds and those that do not.
I have had several roses have hips form with quite a few exogenous seeds, and wondered the same at the time. So I kept track of them and came to two conclusions. #1: Some seed bearers have a proclivity towards producing exogenous seeds. #2: The seeds germinate approximately like other seeds produced by that seed bearer. I think that it might help the seeds if they are not ‘fried’ by all day sun exposure, which leaf cover can provide (I did not try to cover the several hips produced that fell in this catagory, but they were sufficiently early enough to be afforded the luxury of leaf cover, which may have helped. The seed cover is really quite protective by itself, as long as the seed is getting the nourishment it needs to mature. One rose that produces hips with so many seeds that it splits and has exogenous seeds is Lady of the Mist, and even then the seeds have matured and germinated and were quite healthy.
This year I had such a small number of achenes collected, I could afford the luxury / fun (for me) in removing their pericarps before direct sowing (no stratification done).
Most of these exogenous Ebb Tide achenes were easy to spot from the rest of them during the pericarp extractions (as most all had sunburned tips), so it was easy to keep track of what was inside them, and I took particular note for the same reasons you write this post.
I can confirm both exogenous and non-exogenous achenes seemed to contain normal appearing true rose seed @ a similar frequency / rate (approx. 50%). The true rose seeds within the exogenous achenes did not appear any different to my eye compared to their non-exogenous counterparts.
I cannot provide scientific proof that there is never any difference, but my guess is that based on these things (and similar findings from previous seasons as well) it is a possibility that in some cases there might be no significant difference between the two type of achenes.
In any case, I personally don’t treat exogenous achenes any different to any other rose achenes (and wouldn’t even if I should do as I would find it too time consuming / fiddly if there are large numbers involved).
Recall that blackberries and strawberries are in the rose branch of plants. At some time there must have been a rose precursor that had no receptacle. There are even stomates on the surface of the achenes indicating their relation to something leafy. So if they don’t get knocked off by creatures they ought to be fine.
I always thought this was like stuffing 10# into a 5# bag. For any rose that we grow, as far as I can recall the hips are about the same size regardless of the number of seeds in there. We never separated them or treated them any different - just straatified them all and planted them. Never kept any stats to check to see if there is any difference. What with the lousy germination I had the past few years, it it looked like a viable seed it was planted!
I treat all of my seeds the same also. I wondered about exogenous seeds with my first batch and researched about it back then. Everything I heard and read said that they would work ok. Some roses like Violina have mostly exogeneous seeds. I take Joe’s approach and plant everything.
My method of treating all seeds is to put them in a zip-lock sandwich bag with a squirt or 3 of water mixed with 3% hydrogen peroxide at a 10/1 ratio. This keeps them moist and seems to help all the shells break down the same way. I havent separated them but have found germination seems to be the same with both types of seed when from the same parent. Anne-Morrow Lindberg gave me one hip with 106 seeds with about 1/3 being exogenous because the hip split open with the burden of seeds. I really only have one seedling of value from that cross 3 years on… Culling is a necessary evil when space doesn’t allow. I’ve since moved to acreage - let’s see if I am as brutal now I am not taking up the entertaining area with my seedlings (no-one nagging to me cull them).
I never gave it a thought till you brought it up but last year there where a lot of exogenous seeds and a number with split hips and germination occured for the first time on at least one with split hips, not many but at least some. If the exogenous seeds developed early on the hips, they just dried up and on at least one plant the hips didn’t really develop.