A Study of Cotyledon Asymmetry in Cannabis sativa L.

Abstract

Abstract Although it has been known that the two cotyledons of Cannabis sativa L. seedlings tend to differ in size, the development and magnitude of this phenomenon have not previously been described. In the dry seeds, the “outer cotyledon” (remote from the radicle) is about 50% heavier than the “inner cotyledon” (adjacent to the radicle). Two days after germination, the difference in fresh weight has been reduced considerably, but thereafter the outer cotyledon remains slightly more than 20% heavier than the inner. In about one in four seedlings, the tip of the outer (normally the larger) cotyledon is persistently covered by remnants of the seed coat, including a characteristic dark area which enclosed the tips of the cotyledons in the seed. In about one in ten seedlings, the achene shell (pericarp) remains up to several days on the tip of the outer cotyledon. These features serve to confirm the identity of very young seedlings of C. sativa, for which there has not previously been a reliable means of identification. Seeds from several sources did not differ significantly from each other with respect to weight ratio of the cotyledons, nor were there significant differences in cotyledon ratio found when seedlings were grown in darkness, a 16-hour light regime, and in continuous light. Microscopic connections of unknown significance were observed between the adpressed adaxial surfaces of the cotyledons in the seed.