Morphological variation, frequency, and distribution of bisporangiate strobili inPicea mariana

摘要

Investigations of strobilus production over 4 successive years in 8- to 18-year-old plantations ofPicea mariana(Mill.) B.S.P. revealed infrequent occurrence of bisporangiate strobili. However, such strobili were borne only at, or shortly after, the time that the tree first initiated reproductive activity, and mostly at 10 years of age. They were borne terminally or distally on shoots in the microsporangiate zone of the crown and mostly on shoots located near the megasporangiate zone. All bisporangiate strobili had microsporophylls proximally and bracts and ovuliferous scales distally. The proportions of these elements varied and strobili with more microsporophylls than bracts generally abscised after pollen shedding. Some strobili with more bracts than microsporophylls and with a thick curved axis remained on trees and had normal ovuliferous scales but shrivelled microsporophylls and microsporangia.