154 EMBRYOGENESIS IN PLANTS 



in the axis of the archegonium and at right-angles to the axis of the 

 prothallus. The two daughter cells are not quite equal in size, a condi- 

 tion that appears to be general for leptosporangiate ferns. The further 

 embryonic development also appears to be in accord with that of other 

 leptosporangiate ferns. Matonia pectinata has long been of special 

 interest to morphologists because of the presence of a very distinctive 

 polycyclic solenostele in the adult rhizome. Stokey and Atkinson 

 found that in a quite young embryo there is a solid core of xylem at the 

 centre, the conducting tissue being well differentiated before the embryo 

 is large enough to burst through the enlarged venter or calyptra. In 

 this species, in short, there is apparently a precocious development 

 of vascular tissue. The vascular tissue is continuous from below 

 the apices of the shoot and the first leaf backwards to the first 

 root. Fig. 33m. In its general appearance and somewhat massive 

 construction, this embryo is not unlike that of Osumnda cinnamomea. 

 Fig. 33f. 



Dryopteris fiUx-mas. The embryogeny of this classical species was 

 investigated by Hofmeister. More recently Becquerel (1931) has 

 followed the embryonic development by growing prothalh bearing 

 embryos in mineral culture solutions. Several archegonia on the same 

 prothallus may be fertilised and begin to develop embryos ('poly- 

 embryons') but usually all but one abort. However, it is not rare to 

 find two sporophytes on a single prothallus. Vladesco (1935) cultured 

 the prothalli of this fern on burnt soil and noted that the co-existence 

 of several embryos on the same prothallus had no effect in modifying 

 either the orientation or the sequence of the partition walls. He also 

 noted that in some cases the basal wall dividing the zygote was not so 

 much perpendicular to the prothallial axis but strongly inclined towards 

 the prothallial apex. The posterior segment appeared to be the larger 

 of the two segments. In this species, Hofmeister stated that the zygote 

 divided by a basal, a transverse and a median wall in that sequence. 

 Vladesco has corrected this statement and maintains that the second 

 wall is the median wall, as in most leptosporangiate ferns. Moreover, 

 in the posterior segment, the two quadrants may be of unequal size — 

 evidence of biochemical heterogeneity or of unequal forces, e.g. 

 pressures, acting on different sides of the hemisphere. Vladesco has 

 also noted other irregularities in the division of the zygote. Whilst 

 still in the globular post-octant phase, the inception of the several 

 organs begins to be apparent. The first root occupies a median position 

 relative to the first leaf. The foot not only comprises the posterior- 

 superior quadrant, but also part of the anterior-superior quadrant. 

 The general organogenic development is comparable with that of 

 Gymnogramme, Fig. 34. 



