EMBRYOGENESIS IN E US POR ANG I ATE FERNS 133 



It is now well known that when a piece of plant tissue containing a shoot 

 apex is placed in a culture medium, the growth and morphogenetic 

 activity of the apex are greatly enhanced once a root has grown down 

 into the medium. 



From the foregoing analysis it appears that the early embryogeny 

 of O. viilgatunu although seemingly very anomalous, is, in fact, com- 

 parable with that of other ferns, including leptosporangiate ferns, the 

 morphogenetic anomalies being probably referable to nutritional 

 factors. This view is supported by data relating to the inception and 

 organisation of buds on this species (Wardlaw, 1953). 



Organogenesis in Induced Buds. The earliest stages in the formation 

 of buds in roots and shoots afford interesting materials for comparison 

 with the embryogeny. When a bud is formed at the root tip, according 

 to Rostowzew (1891), a cell of the root apical meristem divides several 

 times, its segments forming the apex of the new bud and the first leaf. 

 Root formation takes place some time later, and there may be con- 

 siderable evidence of leaf growth before the first root emerges from the 

 parent-root tissue. When a bud is induced at some point in the mature 

 region of a root, the first stage consists in the development of an 

 ellipsoidal or spherical mass of meristeniatic tissue in the middle or 

 inner cortex. Within this mass a shoot apical meristem becomes 

 organised (Wardlaw, 1953), and soon thereafter the first leaf is formed. 

 The first root may then have its inception, or this may be delayed a 

 little. A considerable amount of leaf growth may take place in the 

 course of a few months. Once a root-tip has been differentiated, root 

 growth may be rapid, so that a thick root, considerably larger than the 

 first leaf, may be formed in 4-6 months. When an endogenous bud is 

 formed in the pith of a decapitated shoot its development is closely 

 comparable with that just described: a shoot apex is first formed; the 

 first leaf is formed almost simultaneously and shows evidence of very 

 rapid growth; the root apex is always the last to be differentiated, but 

 subsequently root growth may be more or less vigorous in different 

 instances. In buds formed laterally on the shoot, a shoot apical meri- 

 stem is first organised; leaf formation follows and some time later 

 a root apex appears. In these induced buds the relation of roots to the 

 leaf-bases cannot be precisely specified (Wardlaw, 1954). 



These induced buds are characterised by the very active formation 

 of densely protoplasmic meristeniatic cells, as compared with the 

 starch-filled cells of the embryo. The buds are also characterised by the 

 early differentiation of a shoot apical meristem, with subsequent or 

 simultaneous leaf formation, and the later inception of roots, whereas, 

 in the embryo, root formation comes first. These differences in organo- 

 genic activities as between embryos and buds can almost certainly be 



