a B 



Fig. 30. Types of segmentation in the zygotes of ferns 

 A Exoscopic embryogeny, as in Ophioglossum vulgaUnn and Botrychium Imaria. 

 the first partition wall defining the shoot (.v) and foot (/) regions; a neck of arche- 

 gonium ; p, prothallus. B, The first wall is again at right angles to the archegonium, 

 but the embryogeny is endoscopic, as in Angiopteris; s, shoot; /, first eat ; /, toot, 

 /■ root C Typical endoscopic embryogeny, as in some Marattiales, the suspensor 

 (su) being next the neck of the archegonium. D, Lateral embryogenic development, 

 as in leplosporangiate ferns, the first wall being in the axis of the archegomum 

 E Diagrammatic representation (after Heinricher) of the disposition of embryos 

 induced on both the upper and lower sides of the cordate prothallus of a lepto- 

 sporangiate fern ; pa and pb indicate the directions of the apex and base respectively 

 of the prothallus. In both archegonia (a), the embryos have the same orientation 

 towards the archegonial neck and the apical region of the prothallus. 



