The American Natulaist

The american naturalist
Evolution and speciation in mosses
As a footnote to the title I have chosen, I should say that the word “mosses” has been used intentionally here in one of its widest and oldest senses, to include peat mosses. More technically, these plants are all called bryophytes, although the formerly more comprehensive category, bryophyta, has recently been given a much restrictedmeaning, about which more will be said later.
A consistent historical trend in the classification of the plant kingdom has been the multiplication of divisions, through the gradual recognition of fundamental differences between groups formerly considered to be rather closely related. From the classification of the plant kingdom proposed by Eichler in 1883, with four divisions, widely accepted ageneration ago, we now have progressed to 24 divisions in one of the more classification, proposed by Bold. Among other innovations, Bold has modified the classical concept of the division bryophitha, which contained both mosses and hepatics, by raising each of the two major former classes, hepaticae and Musci. To the rank of division, the Hepatophyta and the Bryophyta. I view my friend HaroldBold´s treatment with mixed emotions.
As a teacher, I cannot help but deplore the restriction of the time- honored term “Bryophyta”, to mosses alone, because of the confusion that is certaint to result. As a oprofessional bryologist, on the other hand, I can go much further thand Bold has, and with equal justice raise other highly distinctive groups of bryophites to divisional rank. The peat-mosses. OrSphagna, and the hornworts or Anthocerotes are as distinctive in their own ways as are the true mosses and hepatics. On the other hand, in a search for differences, and with strong emphasis placed on distinction, we stand in more than sloight danger of overlooking basisc similarities and relationships. With the gradual but continued devaluation or inflamtion of the rankgeneration discover thatour presently considered groups, diverse and uneasily anchored together today in this “ Superbryophita”, may be widely separated phylogenetically and taxonomically, and actually form centers of other constellations of classification.
Bradley Moore Davis came to Stanford from Indiana unervisity with Douglas Houghton Campbell as his student, and was a member of our first graduating class in 1892.As one of my first botany professors at the university of Michigan, he firmly convinced me that the sporophyte of mosses and hepatics had evolved gradually through the intercalation of an increasing number of mitotic divisions between the fertilized egg or first diploid cell, and meiosis and spore production. While I was a student, Campbell´s sonorous phrase (adapted from bower), that thesporophyte developed phylogenetically through “the progressive sterilization of potentially sporogenous tissue, “ seemed to me apt and logical. Somewhat later, however, I came to understand the persuasive arguments put forth for an opposite point of view, that alternation of generations in higher plantas could possibly represent a much more advanced aspect of the relatively simple isomorphichaplont-diplont situation still found in some green algae, as Ulva , where the sexual and asexual plants are identical but separate.
If we follow this theory, which has found increasing support, we must assume that the earliest bryophyte-like plants must have had sporophytes entirely to nearly independent from the gametophytes and rather similar to each other in appearance. Two of the most interesting bitsof evidence in this direction are also most commonly overlooked; the young sporophytes of all “mosses” are green and from somewhat to highly photosynthetic; moreover, the young sporophyte of true mosses regenerates protonema, presumably a gametophytic structure.
The great morphologists worked with materials preserved in alcohol and other solutions that removed chlorophyll. Consequently the...