spathglottis plicata seeds (i think the stage they're in is called protocorm?)

[estación seca]

Agar gel is composed of algae products that include carbohydrate in their makeup. It might be that orchid seedlings have enzymes that can digest agar to sugars the seedlings can use.

[dansyr]

I can confirm that different agar grades have different amounts of non-agarose compounds that may affect growth - e.g. there's a noticeable compositional difference between "bacto" agar and "molecular biology" grade agar. That being said, I feel like I read somewhere that some orchid lineages actually do develop some limited endosperm, which might be a simpler explanation than impure agarose.

[epiphyte78]

Dansyr, thanks for the info. Initially I was pretty sure that the exceptionally large seeds of the common reed-stem Epidendrums did have an endosperm. I searched around but was unable to find any science to support the possibility. So I e-mailed a couple of experts. One said that the consensus is that orchid seeds don't have an endosperm. The other said the same thing but also said that cotyledons can also supply nutrients. He gave an example of beans... they don't have an endosperm but they do have a relatively large cotyledon. I searched around and found that the following species do have a cotyledon (more or less)...

Arundina graminifolia
Bletilla striata
Dendrochilum glumaceum
Epidendrum vitellinum
Polystachya microbambusa
Sobralia macrantha
Thunia alba

I'm sure that they haven't examined the seeds of every species.

For me it's academic whether an orchid seed has an endosperm or cotyledon. The practical issue is whether any of the seeds have enough nutrients to germinate on their own. Not having to worry about fungus/flasking is no small thing.

Sometimes when I harvest a reed-stem pod the seeds will have green embryos that are visible to the naked eye. Does this mean that they are photosynthetic? Are green peas photosynthetic?