EMBRYOGENESIS IN LEPTOSPORANGI ATE FERNS 163 



maintain embryos so that tiiey produce a succession ot^ the awl-shaped 

 leaves, or of bifid leaves, or they can be induced to form the large 

 tetrafid leaves precociously. Also, plants which have been forming 

 normal tetrafid leaves can be made to produce awl-shaped leaves by 

 appropriate changes in the composition of the culture medium. Closely 

 comparable results have been obtained with Adiaiitum (Wetmore, 

 1950; Wetmore and Wardlaw, 1951). Various departures from the 

 normal development of the leaves and roots of Marsileci can also be 

 induced by the addition of certain growth-regulating substances to the 

 culture media. 



Regeneration. Goebel (1908) showed that if the first leaf of the 

 sporophyte of various ferns is cut off and placed on moist soil, it may 

 either yield an aposporous prothallus, or a bud, or a formation of 

 intermediate or indeterminate character. Relevant data for various 

 fern species are cited by Vladesco (1935). Goebel advanced the view that 

 the kind of regeneration obtained is determined by nutritional factors. 

 Beyerle (1932) held that only when the first leaves of some species were 

 excised could they be induced to form buds or prothalli. The regenera- 

 tions originate from epidermal cells and may arise at various points; 

 the smaller the leaf, the more will it tend to yield a prothallus rather 

 than a bud. Also, external conditions do not, apparently, modify the 

 nature of the regeneration. 



In studies of regeneration, Vladesco (1935) used young sporophytes 

 of Gynmogramme sidphurea and found : (i) that isolated first or second 

 leaves, excised a little above their junction with the shoot, and placed 

 on moist soil, did not form buds ; (ii) that a phyllorhize (i.e. a leaf and 

 its attached root) without attached stem tissue, when planted in moist 

 soil, also failed to yield buds ; (iii) that a very young first leaf, excised 

 so that the shoot apex remained attached to it, yielded an almost 

 normal plantling; the root formed in conjunction with the second leaf 

 anchoring the plant to the soil ; (iv) that the removal of the first root 

 did not greatly affect the subsequent development of the embryo, an 

 unusually robust second root being formed precociously; (v) that the 

 removal of the first leaf led to a reduction in the size and to a simplifica- 

 tion of the second leaf, and to a suppression of the second root; (vi) 

 that the removal of the first leaf and first root was followed by the 

 formation of the second leaf and its root, both being somewhat reduced; 

 (vii) that when the shoot apex was excised, about the level of the anterior 

 region of the foot, there was regeneration at the cut surface of both foot 

 and vascular strand, the organisation of one or more new meristems, 

 and the subsequent development of one or more buds and small 

 plantlings. When very young embryos, still without vascular develop- 

 ment, were cut so as to remove the apical portion, the root primordium 



