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Chapter VII 



EMBRYOGENESIS IN THE LYCOPODINEAE: 

 LYCOPODIUM AND PHYLLOGLOSSUM 



GENERAL ACCOUNT 



HE initial stages in the embryogeny of all species of Lycopodium and 

 _ of PhyllogJossum are closely comparable. The venter of the 

 archegonium is in cellular continuity with the prothaUial tissue. At 

 the first division of the zygote a transverse wall is formed and the 

 polarity of the embryo is determined. The cell next the archegonium 

 neck remains undivided, or divides only occasionally, and is known as 

 the suspeusor; the inner or embryonic cell gives rise to the embryo 

 proper. The embryogeny is thus typically endoscopic. The embryonic 

 cell then divides by transverse and longitudinal walls to form two 

 quadrants of cells. The hypobasal quadrant, contiguous with the sus- 

 pensor, gives rise to a parenchymatous foot; the epibasal quadrant 

 forms the distal meristem and first root. As the embryo grows it 

 becomes deeply embedded in the tissue of the prothallus. In different 

 species, as the embryogeny progresses, characteristic differences become 

 evident. This is largely due to the fact that different regions of the 

 embryo may undergo a considerable relative enlargement: in some, 

 a conspicuous foot is formed; in others, a modified tuberous shoot 

 known as a 'protocornV develops; while, in yet others, localised 

 swellings do not occur (Treub, 1884, 1886, 1890; Bruchmann, 1910). 



LYCOPODIUM SELAGO AND L. PHLEGMARIA 



The prothallus of L. selago may be subterranean or superficial and 

 varies from an elongated, cylindrical structure in firm soil to a more 

 compressed and flattened one at or near the soil surface. Its nutrition 

 is mainly mycorrhizic, though some green pigment develops in prothalli 

 exposed to the light. The prothallus of L. phlegman'a is an attenuated 

 and repeatedly branched structure and is entirely subterranean and 

 saprophytic. 



In these, as in other species, the polarity of the embryo is apparently 

 determined by internal factors and not by gravity or factors in the 

 external environment. In Lycopodium selago, Fig. 22a-d, the embryonic 

 cell divides by two vertical walls at right-angles to each other, the 

 ensuing transverse division thus yielding an eight-celled embryo. The 

 further longitudinal, transverse and periclinal divisions take place with 



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