EMBRYOGENESIS IN EUS POR ANGF ATE FERNS 141 



the apex to the first and has a vascular strand which becomes conjoined 

 with the first leaf-root strand; and, as Campbell (191 1, 1921, 1940) and 

 others have shown in some detail, the vascular system subsequently 

 developed in the young sporophyte shoot is apparently composed 

 entirely of decurrent, fused leaf-traces. This seems to be true in all 

 Marattiaceae so far studied; i.e. there appears to be no true axial or 

 cauline stele, and the primary stele at the base of the shoot is not a 

 true protostele. However, in Danaea, after the formation of about the 

 seventh leaf, a single axial strand which is not of foliar origin can be 

 traced in the pith to the shoot apical meristem (Brebner, 1896, 1902; 

 Campbell, 1940). 



Campbell has called attention to the insignificant size of the shoot 

 apex in embryos of Marattiaceae, and to its belated appearance in the 

 Ophioglossaceae. In his view, the shoot largely consists of coalescent 

 leaf-bases, and in this he sees some confirmation of Delpino's theory 

 that the leaves and not the stem are the primary organs, the so-called 

 stem being an integrated construction of foliar members. The same 

 idea underlies the various phytonic theories of shoot construction, 

 Campbell (1921) further states that the young sporophyte of Ophio- 

 glossum iias no stem at all, but consists simply of a single leaf and root, 

 the stem arising secondarily as an adventitious bud.' While it is true 

 that the leaves are the rapidly-growing and conspicuous organs in 

 eusporangiate ferns — as indeed they are in all ferns — nevertheless we 

 may note that, however insignificant histologically the shoot apex may 

 be, and however late its appearance in the embryogeny, it is the centre 

 and focus of the whole axial development, all the lateral members 

 being formed in an orderly manner in relation to each other round 

 that centre. Moreover, if the apex is destroyed the axial growth and 

 the formation of new foliar members soon ceases (Wardlaw, 1949a). 



The suspensor in Danaea is small; in Macroglossum it is large. 

 The presence or absence of a suspensor in the Marattiaceae does not 

 change the orientation of the embryo: it is always endoscopic and 

 directed upwards through the prothallus. In the particular case of 

 Macroglossum, Bower (1935, p. 529) remarks that the peculiar form 

 assumed by the embryo 'gives the impression of its being held in place 

 by its suspensor, but unable to penetrate the prothallus upwards. . . .' 

 'Possibly such difficulties as its form implies may have opened the way 

 for the condition constantly seen in the leptosporangiate ferns, where 

 the embryo without a suspensor emerges on the lower surface of the 

 prothallus.' Angiopteris evecta is of interest in that it has been described 

 as being with and without a suspensor in different specimens, Fig. 

 32a, b, e (Land, 1923). (For a general discussion of fern embryos, see 

 end of Chapter X.) 



