COMPARATIVE MORPHOGENESIS OF CYPRIPEDIUM ACAULE (ORCHIDAECEAE) PROTOCORMS CULTIVATED IN-VITRO WITH OR WITHOUT SUGAR

Seeds of the terrestrial orchid Cypripedium acaule from temperate regi ons contain an undifferentiated embryo consisting of about one hundred cells. These cells contain lipid and protein storage reserves. The de velopment of the seeds was studied in vitro on a germination medium wi th or without dextrose (glucose). On the medium containing dextrose, p roembryos develop and form a protocorm. From the anterior pole of the protocorm appears a ''promeristem'', a structure that will form a scal e and the apex of the seedling. The formation of the root never preced es that of the apex. In the protocorm, the amount and size of starch g rains show an increasing antero-posterior gradient. Only the apex, the procambium. and the secretory cells do not accumulate starch grains. On the medium without dextrose, the proembryos develop slowly into a p rotocorm, and a semi-meristematic region can be recognized at the ante rior pole. However, no other tissue differentiation occurs and the pro tocorm soon degenerates without having undergone organogenesis. The pr otocorm accumulates a few starch grains, more voluminous and more nume rous at the posterior pole, that agglomerate around the nucleus; but d uring the development, these rapidly disappear from the cells. General ly, all cells are strongly vacuolated. These observations indicate tha t orchid seeds cannot reach the seedling stage without a sugar input, which is ensured by a fungal symbiont in nature.