When the aleurone layers were separated from germinating whole grains and incubated in 10 millimolar CaCl₂, the α-amylase activity in the medium increased linearly for about 30 to 60 minutes, indicating secretion. The activity inside the aleurone layer decreased only slightly during the incubation, indicating that secretion of α-amylase was accompanied by synthesis. The rates of secretion in vitro by the aleurone layers separated at different stages of germination corresponded rather well to the rate of accumulation of α-amylase activity in the starchy endosperm in a whole grain.

Scutella separated after 1 day of germination released small amounts of α-amylase activity into 10 millimolar CaCl₂. This release was linear for at least 1 hour and did not occur at 0°C; it is therefore likely to be due to secretion. At later stages of germination, the secretion by the scutella was slower than at day 1 and the total secretion accounted for only 5 to 10% of the increase of α-amylase activity in the starchy endosperm in a whole grain.

Since the times from the separation of the parts of the grain to the beginning of the secretion assay (10-40 minutes) as well as the duration of the assay itself (20-60 minutes) were short, the rates of secretion by the separated grain parts are likely to represent those in an intact grain. The results indicate therefore that at least in the conditions used the bulk of the total α-amylase in the starchy endosperm is secreted by the aleurone layer, the contribution by the scutellum being only 5 to 10% of the total activity.