162 EMBRYOGENESIS IN PLANTS 



growing on the surface of the cukure liquid. These latter sporophytes 

 were closely comparable with those produced on burnt soil, except that 

 the first leaf was of smaller size and simpler form; the succeeding 

 leaves were also reduced and they had no attendant roots, i.e. plantlings 

 with several leaves had but a single root. In submerged plantlings the 

 first leaf gave rise to aposporous prothalli, while the second leaf 

 developed into an indefinite organ, intermediate in character between 

 a leaf and a prothallus. When such plantlings were placed on moist soil, 

 the shoot apex renewed its normal activity and new leaf and root 

 primordia were formed. When zygotes of Dryopteris parasitica were 

 cultured in solutions under various conditions, and in various positions, 

 the orientation of the embryo in the archegonium was not altered 

 (Vladesco, 1935). Plants grown on cotton wool, kept continuously 

 moist with culture solution, developed one root for each leaf: prothalli 

 floating at the surface of the same solution, on the other hand, bore 

 embryos which developed very slowly, were of smaller stature, and 

 showed a diminution in the number of roots : and submerged plantlings 

 were still more reduced. Submerged plantlings of this species, however, 

 yielded no aposporous prothalli. In Ceratopteris thalictroides, an 

 aquatic species, the plantlings produced on floating prothalU were 

 almost as vigorous as those obtained on moist soil, but there was some 

 reduction in size in those which developed fully submerged. In all these 

 cultures of Ceratopteris, leaf formation was accompanied by root 

 formation — exemplifying the phyllorhize condition in its classic form. 



Some interesting correlations between the supply of nutrients, 

 including sugars, nitrogen-containing compounds, vitamins, growth- 

 regulating substances, etc., and morphogenesis in older embryos, have 

 been established by Allsopp (1950, 1951, 1952, 1953) and Wetmore 

 (1950, 1951). 



In Marsilea the first leaf is small, non-laminate and awl-shaped, 

 but those subsequently formed show a progressive increase in size and 

 form bifid and tetrafid laminae. This kind of observation has been 

 regarded as supporting the theory of recapitulation. Goebel (1908) 

 pointed out that the primordia of the young fern sporophyte and of the 

 adult plant are essentially alike, and that the size and complexity of the 

 fully developed leaf are the direct result of the nutritional status of the 

 subtending apex. This view is now supported by a considerable body 

 of evidence (Wetmore and Wardlaw, 1951; Wardlaw, 1952). By 

 growing young embryos of Marsilea dnimmondii and other species in 

 sterile media, using the methods of tissue culture, Aflsopp (1951, 1952, 

 1953) has shown that the rate of growth of the embryo, and the size and 

 complexity of its leaves, are primarily determined by the supply of 

 nutrients. By varying the concentration of sugar, it is possible to 



