Factors Breaking Vegetative Dormancy in Certain Mosses

Periodicity in the growth of many mosses is well known to bryologists. The latest description of this was made by Hagerup (1935). As Hagerup pointed out, many temperate zone mosses are vegetatively dormant during the late summer and fall. Sexual reproduction and vegetative growth in many are initiated in early winter to early spring. The experiment described below attempts to ascertain whether day length or low temperature or both are involved in the summer-fall vegetative dormancy. A random group of mosses was first collected and planted on sand overlying peat in the college greenhouse during the middle and last part of October 1960, before the weather had cooled to the point of frost. The plants were placed on a bench and illuminated by two goose-neck lamps with 75-watt bulbs connected to a time clock so regulated as to supplement light to a 16-hour day. The lamps were straightened and placed outside of the 2 X 5 foot area they illuminated to reduce their effective heat to a minimum. Duplicates of the above mosses were planted in the same substratum under a bench protected by its position from artificial light in the greenhouse. This bed had a southern exposure and received, during the day, approximately the same amount of sunlight as the other. This bed was exposed to the seasonal day length. The greenhouse is shielded from early morning and late afternoon sun, and it is estimated that the effective day length here varied from approximately eight hours in December to ten in March. The plants at both sites were regularly watered lightly but allowed to become dry between waterings. At the same time, five duplicates of the above mosses were planted in the two sites for testing with a gibberellin. On January 11, 1961, duplicates of most of the above mosses were gathered again and planted alongside the former specimens at the two sites, These had been exposed to an effective period of frost or freezing for about 50 days. Careful examinations for growth were made with handlens or low power binocular microscope on January 13, March 6, and April 11, 1961. Three species, Brotherella tenuirostris, Dicranum scoparium, and Haplohymenium triste, were not collected again in January