. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 204 SYMMETRY OF THE SPOROPHYTE those relatively few cases among Bryophytes where the radial symmetry is departed from. Among the Liverworts the only recorded example of departure from the radial symmetry is that of Monoclea : here the sporogonial head, which is borne upon a cylindrical seta, is curved over to one side, and it dehisces along the upper surface by a longitudinal slit, the whole capsule widening out later into a spoon-like form. Examination of developmental stages shows that the young spo
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 204 SYMMETRY OF THE SPOROPHYTE those relatively few cases among Bryophytes where the radial symmetry is departed from. Among the Liverworts the only recorded example of departure from the radial symmetry is that of Monoclea : here the sporogonial head, which is borne upon a cylindrical seta, is curved over to one side, and it dehisces along the upper surface by a longitudinal slit, the whole capsule widening out later into a spoon-like form. Examination of developmental stages shows that the young sporogonial head is cylindrical in structure. The accepted version of this is that the capsule is developmental!}' four-valved, but that dehiscence is by one slit only, and accord- ingly that the four valves remain coherent; but transverse sections of the mature capsule show no evidence of a structural dorsi- ventrality: the transverse section is radial up to maturity, and there is no apparent structural provision for dehiscence. The natural conclusion will be that Monoclea shows only a slight, and ontogenetically late and unimportant deviation from the usual radial type. There are no observations connecting this with external causes. The sporogonia of most Mosses are also of the radial type throughout; but in a considerable number a more or less marked dorsiventrality is seen in the mature condition. The radial construction is as a rule accurately maintained in those sporogonia which grow vertically upwards, such as Sphagnum Phascum, or Orthotrichum, and all sides appear equally developed in the longitudinal section (Fig. 103. 3). But in many an unequal development is found, which is in relation to the position which they assume. As maturity is approached they curve to one side, and the capsule becomes oblique, or may even hang over. In these cases the earlier stages of the sporogonium are radially constructed, but an inequality appears on the two sides, with, it may be, a slight
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