. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. MARCHANTIALES 261 may be taken as a fair example (Fig. 121), is more complex than that of the Ricciaceae in having polarity of structure, and differentiation of the internal mass of sporogenous cells. Both these characteristics suggest further steps in sterilisation of potentially fertile cells. The polarity is marked in the more or less oblong external form, but more definitely by the fact that the basal tissue is sterile, and develops as the foot. ' "H. Sporogonium of Fegatella (Conocepha
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. MARCHANTIALES 261 may be taken as a fair example (Fig. 121), is more complex than that of the Ricciaceae in having polarity of structure, and differentiation of the internal mass of sporogenous cells. Both these characteristics suggest further steps in sterilisation of potentially fertile cells. The polarity is marked in the more or less oblong external form, but more definitely by the fact that the basal tissue is sterile, and develops as the foot. ' "H. Sporogonium of Fegatella (Conocephalits). I., venter of fertilised archegonium with eight-celled embryo. II., transverse section of a similar embryo. III., IV., older em- bryos in longitudinal section. V., part of a longitudinal section of a developing capsule, showing differentiation of archesporial tissue into elater-forming cells (el), and sporogenous cells (sp). VI., part of longitudinal section of receptacle with embryo. VII., similar section showing two mature sporogonia in outline. *K-=air-chambers; cfl/=calyptra; ;_/==foot; «=neck of archegonium ; ^=pore; rec. st. =stalk of receptacle ; r^/z. =rhizoids; j=setaofsporogonium. (AfterCavers.) which supports the fertile capsule (Fig. 121, vn.). It is stated that the whole hypobasal half of the zygote is thus sterile, though this limitation may not apply for all cases. This state as compared with that of Riccia might be expressed as a consequence of sterilisation of the whole product of the hypobasal half of the zygote; but it is still a matter for debate whether the Ricciaceae really represent the progenitors of the Mar- chantiaceae. The presence of this polarity may be held as a biological concomitant of the position of these larger sporogonia relatively to the thallus which bears them: the spherical form of Riccia is suitable to its. Please note that these images are extracted from scanned page images that may hav
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