Dorety (1908), Chamberlain (1919, 1935), Hooft (1970), Bierhorst (1971), Rao (1971), Pant and Sing (1991), and Foster and Gifford (1974) all agreed that cycad seedlings have a coleorhiza. Stevenson (1990, page 20), however, is of the opinion that a tree coleorhiza is unique to the grasses and that cycads do not have a true coleorhiza.
During germination, the elongating embryo rips a circular segment from the perisperm which can sometimes be seen as a cap on the apex of the 'coleorhiza' as it emerges from the sclerotesta (Fig.
Therefore, there is no true hypocotyl unless the very short part of the radicle between the cotyledonary plate and the attachment of the 'coleorhiza' to the radicle (Fig.
The columella may also be easily misinterpreted as a 'coleorhiza'.
This study investigates cold responses of Ot220 and America during seed germination, at the phases of coleorhiza (1-2 mm elongation) and radicle (10 mm elongation) emergence, and compares these responses with those reported for later developmental stages of these cultivars.
Seed imbibition was initiated by adding 8 mL of distilled water, and seeds were maintained in the dark at constant temperature regimes (0, 3, 6, 10, or 17 [degrees] C) until embryo elongation (radicle or coleorhiza).
Sensitivity to low temperatures was evaluated by the following parameters: (i) the number of days to the initiation of coleorhiza emergence (Di), (i) the number of days for 50% of the seed population to germinate ([D.sub.50]), and (iii) the final percentage of germinated seeds after 15 d.
The root apex is initially covered by a coleorhiza
, and the
Germinating seed (coleorhiza
protruding) were counted and removed Monday, Wednesday, and Friday (beginning on Day 5) for a 28-d period.