Seasonal growth and development of sporophytes in wild populations of Pogonatum and Polytrichum species

Abstract

The contribution made by the apical cell to the growth of the sporophyte in Pogonatum and Polytrichum species was determined by counting the products of segmentation of the apical cell as they accumulated until an end point was reached. In both subgenera cell division had ceased in the apical cell when the sporophyte was about 0.7 mm long or about 3 weeks old. Thereafter segment boundaries were used to calibrate the apical meristem and to measure the growth of its parts. In the apical meristem there was an excess of segments over the number used to form the capsule. In Polytrichum growth in length of the apical meristem was arrested throughout June and until early October. Meanwhile the seta continued to grow by intercalary processes. When growth of the segmented region was resumed in the autumn, differentiation of the capsule occurred. In Pogonatum there was no arrest of apical growth and no delay in forming a capsule, and the sporogonia approached mature size towards the end of the first growing season. The period of summer rest or quiescence allowed the apical meristem of Polytrichum a prolonged vegetative period. There is evidence that reproduction is subject to climatic stimuli and that postponement of.the development of sporangia is widespread amongst Eubrya.