I20 MARATTIACEAE [ch. 



The gametangia are borne as a rule upon the lower surface, though 

 occasionally observed upon the upper also (Jonkman). They are of a sunken 

 type as usual in Eusporangiate Ferns. The antheridia agree very closel)- 

 with those of Ophioglossmn, but with fewer spermatocytes (Fig 411), and 

 they open by an opercular cell, which is usually thrown off when the 

 antheridium ruptures. The spermatozoids o{ Angiopteris and Marattia zXo'&^y 

 resemble those of Leptosporangiate Ferns, but those of Christensenia are 

 more like those of OphioglossiiDi. The archegonia of the family are also like 

 those of Ophioglossiim, having a very slightly developed neck. The central 

 series is as usual in Ferns; but the ventral-canal-cell, difficult to see in 

 Ophioglossmn, is large and conspicuous, except in Danaea where the same 

 difficulty arises. 



Embryology 



A marked feature of the young sporophyte of the Marattiaceae is that the 

 basal wall is always in a plane at right angles to the axis of the archegonium. 

 The polarity of the embryo is defined by its very first segmentation, and 

 the embryogeny is endoscopic. This is the exact reverse of that in Ophio- 

 glossmn and Eu-Botrycliiian, in which the neck of the archegonium points 

 upwards, and the embryogeny is exoscopic. The difference probably arises 

 in relation to the fact that in the Marattiaceae the archegonium faces 

 downwards, in the Ophioglossaceae obliquely upwards. The effect is that 

 the shoot emerges by bursting through the upper surface of the prothallus, 

 instead of below as in the Leptosporangiate Ferns. Further, the root will 

 naturally point directly downwards (Fig. 410, G, H). If a series of the 

 embryos of various genera of the Marattiaceae were orientated as the}- 

 would be in nature, with the basal wall {b, b) horizontal, they would appear 

 as in Fig. 412. In those o{ Danaea jamaicensis there is a minute suspensor, 

 which is directed downward, towards the neck of the archegonium. In others 

 there is none {Marattia and Angiopteris as a rule). But Campbell has found 

 a suspensor also in Macroglossnm (Fig. 413), while Land has described how 

 in material oi Angiopteris collected on the Island of Tutuila some specimens, 

 but not all, showed an embryo with a suspensor, though other observers had 

 repeatedly described and drawn its embryo without one (Fig. 414). Thus it 

 is clear that in the Marattiaceae there is an inconstancy in respect of the 

 suspensor similar to that seen in the Ophioglossaceae. These facts have 

 prompted som.e to the opinion that the suspensor is an organ formed as bio- 

 logical occasion demands. But on the other hand the opinion seems more 

 probable that where it is present it is in general to be held as primitive; and 

 in particular it is to be remembered that it is absent from all Leptosporangiate 

 Ferns. A still wider comparison has given ground for the opinion developed 

 in Vol. I, Chapter XV, that the suspensor is a vestigial organ, and that plants 



