EMBRYOGENESIS IN EUSPOR ANGI ATE FERNS 139 



would be necessary in order to secure an upright orientation of the 

 shoot except in certain favourable cases.' It does seem probable that 

 the suspensor is a primiti\e feature in ferns, but whether its presence 

 has been as disadvantageous as Bower suggests is debatable. In 

 gymnosperms and angiosperms, which are the most successful and 

 progressive members of the Plant Kingdom, a suspensor has been 

 retained throughout. The same is true of the large and successful genus 

 Selaginella. From the evolutionary, genetical and causal points of 

 view, the loss of a suspensor in difterent lines of descent is, of course, 

 a matter of very considerable interest. For if the suspensor is ultimately 

 a gene-determined organ, then, in different phyletic lines not closely 

 related, there has been the same or a very similar kind of modification 

 in the reaction system. 



MARATTIACEAE 



In these ferns the prothallus is superficial, green and fleshy, but it 

 also has a mycorrhizic fungus in its tissue. The archegonia project 

 downwards from the lower side of the prothallus, and, according to the 

 species, the embryo may or may not have a suspensor. The first wall 

 in the zygote is at right-angles to the archegonial neck and the embryo- 

 geny is vertical and endoscopic, whether a suspensor is present or not. 

 The inner or epibasal segment gives rise to a large first leaf and to a 

 somewhat insignificant shoot apex. The hypobasal segment gives rise 

 to the foot. The primary root, which is usually formed some time after 

 the first leaf, arises endogenously below it from the central tissue of the 

 embryo. Although the shoot apex is inconspicuous and slow to develop, 

 the first leaf is a dorsiventral structure with a normal orientation 

 towards the apex. With some variations, then, the Marattiaceae are 

 like the Ophioglossaceae and other ferns in respect of their funda- 

 mental embryonic pattern. 



In all Marattiaceae thus far investigated {see Campbell, 1911, 1940, 

 for a general survey) the zygote is divided by a transverse wall. In those 

 species in which the segment adjacent to the archegonial neck does not 

 develop into a suspensor, the next wall is at right-angles to the first 

 yielding a regular quadrant stage. In Angiopteris, Marattia and 

 Kaulfussia, the hypobasal cell, lying next the archegonial neck, gives 

 rise to the foot, while the epibasal cell forms the stem apex and first 

 leaf. The latter is the conspicuous organ. Figs. 30, 32, but close to its 

 inner base the inconspicuous shoot apex, with a single 3- or 4-sided 

 apical cell, is also present. On further growth the first leaf bursts 

 through the upper surface of the prothallus. Campbell (1940) regards 

 this stage as being comparable with that of Ophioglossum mohiccamun, 

 except that the apex in the Marattiaceae is more conspicuous. 



