164 EMBRYOGENESIS IN PLANTS 



continued to develop whilst the cut surface developed several ill- 

 defined meristematic outgrowths: some of these became inhibited or 

 abortive, but two or three of them became organised as buds, each with 

 a leaf, the vascular strand of which extended to the primary root. In 

 some cases a single bud became predominant. Excellent regeneration 

 was obtained with very young embryos of Cibotium sp. 



Young Sporophytes and Induced Buds. The young sporophyte of 

 leptosporangiate ferns is typically protostelic, i.e. with a solid xylem 

 core surrounded by phloem and pericycle. During the ontogenetic 

 obconical enlargement of the shoot, the stele enlarges, becomes 

 medullated, then solenostelic, with characteristic leaf-gaps in the 

 cylindrical vascular column, and eventually dictyostelic or meshlike, 

 as new leaves are formed in close phyllotactic sequence on the shoot. 

 In lateral shoots, which are either formed normally or can be induced, 

 the progressive stelar elaboration is closely comparable with that of the 

 developing sporophyte (Wardlaw, 1943 etc.; 1952). This is especially 

 true of the small lateral shoots formed from bud rudiments, or detached 

 meristems (Wardlaw, 1943), in old, mature regions of the shoot: the 

 base of the lateral shoot is typically protostelic, and the first leaves are 

 small and simple with a transition of more elaborate adult leaves as the 

 shoot increases in size. On the other hand, when lateral buds are 

 induced to develop close to the large shoot apex in Dryopteris aristata, they 

 are of large size and solenostelic from the outset and have leaves which, 

 though still small, have some of the elaborate pinnation characteristic 

 of adult leaves. In short, as in the nutritional experiments with embryos 

 of Marsilea, the morphology and anatomy of natural or induced buds 

 reflect the nutritional status of the tissue region from which they are 

 formed. A considerable body of experimental evidence supports this 

 conclusion. Such findings impose caution on the application of the 

 theory of recapitulation to plants {see also Chapter XVI). 



GENERAL DISCUSSION OF FERN EMBRYOGENY 



Zygote and Embryo Organisation. Woodger (1945) has emphasised 

 the need for a theory of zygote structure to explain embryological 

 data. This theory would include concepts relating to cytoplasmic 

 organisation. In his view, the early stages in embryo development are 

 to be explained in terms of the production and mutual interaction of 

 parts — 'of cell parts in the first instance, of cells and cellular parts later.' 



A study of zygote development in ferns suggests the existence of 

 biochemical pattern in the zygote and at the two-celled and quadrant 

 stages. By inference, a heterogeneous distribution of metabolites 

 may already have taken place in the egg before fertilisation. While 

 the cells surrounding the venter may be closely comparable in their 



