I've got some lupine seeds with me, and the instructions tell me to start it in a bath of hot water 180 - 200 F.
Everything I know about, um, basic biology, tells me that this will cook the seeds. But supposedly it's to soften the seed coat so it can sprout through.
Is this actually good advice for lupines? How do they...survive?
I have never hot-water scarified seeds myself, you just got me curious. One thing that startled me was that I could not find any species that absolutely required hot stratification to germinate a seed. All species I saw that benefit from hot water could germinate (less successfully) without it and would also benefit from other, cold, stratification methods.
Using Iliamna rivularis as an example:
The control treatment (intact seeds) yielded poor germination (1.8%). Mechanical scarification (part of the seedcoat removed) improved germination (average germination 49%), but not as much as the combination of boiling the seeds for 120 s plus stratifying them 28 d at 4 °C (average germination 70%). Germinants from the boiling plus stratification treatment appeared to be more vigorous. Impermeability of the seedcoat is the main factor preventing germination, but the response of embryos to stratification may suggest some physiological dormancy.
They only boiled the seeds for 2 minutes. Limiting the heat exposure is a common theme with hot water stratification.
The water temperature should be about 82 degrees Celsius. Soak the seeds until the water cools.
Hot water treatment can be accomplished by dropping seeds in water that has just begun to boil. Remove the boiling water container from the heat source and allow the seeds to soak for 1 to 10 minutes depending on the seed type. Too long an exposure to the hot water can kill the seed.
The rupturing of the seed coat may be induced by heat from fire [10] enabling water to enter the seed and start the process of germination. Many studies have confirmed a release of legume seeds from dormancy after fire [10-17]. Fire temperature or intensity also has an effect on the germination of seeds [17,18] and low intensity fires may not be enough to break dormancy of hard-seeded legumes [19]. In other cases The rupturing of the seed coat may be induced by heat from fire [10] enabling water to enter the seed and start the process of germination. Many studies have confirmed a release of legume seeds from dormancy after fire [10-17]. Fire temperature or intensity also has an effect on the germination of seeds [17,18] and low intensity fires may not be enough to break dormancy of hard-seeded legumes [19]. In other cases lower fire temperatures are preferable for germination with an increase in fire temperature causing seed mortality [18]. [18].
Getting to brass tacks, SEED GERMINATION THEORY AND PRACTICE by Dr. Norman C. Deno (First Supplement) (Second Supplement)
Many Fabaceae (legumes), a few Malvaceae, and a few other species use impervious seed coats as the mechanism for preventing germination before the seed is dispersed. It is not clear whether the mechanism operates by excluding water or oxygen or both, but what is clear is that grinding whole through the seed coat• produces a dramatic effect with the seeds germinating in a few days after puncturing the seed coats and placing in moist media. ... The dramatic effects of such pretreatment of the seed is shown in Table 9-1 at the end of this Chapter. The favorable effects on germination induced by various grinding and abrasion procedures has long been known. This subject is treated in recent books under the title scarification. This term should be promptly abandoned because producing a scar on the seed coat surface has no effect. Only the formation of a true water channel and hole through the seed coat will reliably and reproducibly give immediate germination. ... It has often been recommended to soak seeds of this type in hot water or to pour hot or boiling water over the seeds. An example taken from the Thompson and Morgan catalog is to immerse seeds of Mimosa pudica in 140 deg. F water for twenty minutes. I have verified the effectiveness of this procedure. Prof. Roger Koide at Pennsylvania State University has found that ten minutes in water at 140 is effective for Abutilon theophrasti. The Thompson and Morgan catalog recommends soaking in hot water for a number of species, and it can be inferred that these have impervious seed coats. There are two problems with these hot water treatments. The optimum conditions vary with each species and have to be determined, and the results are generally less effective than physically producing the hole in the seed coat as shown below by the results with Gymnocladus dioica. The hot water treatments work because the heat causes expansion of the seed coats. This causes microfissures to form and in effect a hole has been produced in the seed coat. The extensive studies described below on Gymnocladus dioica are all in accord with this interpretation. Inferences in the literature that the soaking softens the seed coat are incorrect, although the seed coats then soften in a day or two due to enzymes secreted by the activated seed.
So, how do the seeds survive?
Intuitively I think of times I've placed my hands in too-hot water for several seconds and been fine afterwards. Like making mozzarella.
