Paul M. Patterson

Problems Presented by Bryophytic Xerophytism

Since early this year when I learned that a symposium on the experimental ecology of bryophytes would be held at the Tenth International Botanical Congress, I have been aided by many people in my plan initiated then to publish this symposium in TmHE BRYOLOGIST. I now thank my colleagues whose help has made the publication possible. Aside from the credit that he deserves for organizing the symposium, DR. ARTHUR J. WILLIS of the University of Bristol merits high thanks for much of the most rigorous preliminary editing of the manuscripts which he somehow coaxed the participants of the symposium to bring with them to Edinburgh. He was able to clarify many obscure points in the papers through hours of direct discussion with the authors. I know that the authors whose papers were improved through his kind assistance join me in thanking him. The prompt publication of this symposium is in no small part due to his efforts. PROFESSOR PAUL W. RICHARDS, who ably presided at the symposium and conducted the associated discussion, has given me helpful advice on the arrangement of certain material and the improvement of the presentation of some of the papers. And Miss BETTY KLEPPER Of Duke University has helped me in editing and clarifying the expression of certain physiological passages. During the symposium there was a lively discussion after each paper. The speakers in these impromtu discussions were invited to summarize their comments for inclusion in the present publication. Unfortunately the response to this invitation was erratic, and I have decided that to publish the few comments which I have would give a very inaccurate impression of the discussion which actually took place. I thank those participants who composed their remarks and sent them to me. Even though their words are unpublished here, it may be of some small gratification for them to know that in more than one instance their notes helped me in editing the papers upon which they had commented. Lastly I want to thank the seven authors themselves. The congenial cooperation of each one has made the editing of this symposium a small part of the job that it might have been had their spirit of cheerful compromise been less. The papers are published in the order in which they were read in during the symposium held in Hume Tower, University of Edinburgh, August 11.W.L.C.

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

The Effect of Indole-3-Acetic Acid on Certain Growth Phases in Bryophytes

vate, the innovations being soon fertile, and again innovating, thus typically resulting in apparently superficially continuous lateral axes bearing juxtaposed and serially arranged gynoecia. Such a superficially similar arrangement is also characteristic of Schusteria, in which it is arrived at in a fundamentally different manner: the leading (not secondary!) leafy axes produce, along one side of the stem, repeated short gynoecial branches bearing a single leaf, then cutting off the bracteole and bracts. These gynoecial branches are so short that it could easily be assumed that they do not exist and that, therefore, pseudolateral gynoecia of the Taxilejeuneatype are at hand. However, this is not the case; the gynoecia actually occur singly on exceedingly abbreviated lateral branches and are thus truly lateral rather than pseudolateral. In this respect, Schusteria resembles Cladiantholejeunea Herz., a genus to which no close affinities exist.