hypogean

With dicotyledonous seeds, after the protrusion of the radicle, the hypocotyl breaks through the seed-coats; but if the cotyledons are hypogean, it is the epicotyl which breaks forth.

From The Power of Movement in Plants by Charles Darwin

When the cotyledons are hypogean, that is, remain buried in the soil, the hypocotyl is hardly developed, and the epicotyl or plumule rises in like manner as an arch through the ground.

From The Power of Movement in Plants by Charles Darwin

Michalet also says that they are often hypogean.

From The Different Forms of Flowers on Plants of the Same Species by Charles Darwin

In consequence of this injury it had emitted near the hypogean cotyledons two secondary shoots, and it was remarkable that both of these were arched, like the normal epicotyl in ordinary cases.

From The Power of Movement in Plants by Charles Darwin

Long glass tubes, open at both ends, are useful in many other ways, especially in the rearing and study of the smaller hypogean insects or those which bore and live in the stems of plants.

From Directions for Collecting and Preserving Insects by C. V. Riley