EMBRYOGENESIS IN FLOWERING PLANTS 257 



instances of schizocotyly : however, tricotyledons are known to occur 

 in species of Persoonia (Proteales : Proteaceae), Nuytsia and Loranthus 

 (Compton, 1913) and in Eugenia hooked (Myrtales: Myrtaceae) 

 (Johnson, 1936). 



The Ceratophyllaceae and Nymphaeaceae are similar in their 

 embryogeny : in both the suspensor is absent and the maturing embryo 

 is characteristically many-celled and bulky. 



In Grevillea robusta (Proteaceae) the division of the zygote begins 

 rather late when the endosperm is well developed. The first division 

 is by a transverse wall, but no suspensor is formed. The next division 

 is at right angles to the first and on further, approximately rectangular, 

 divisions the embryo becomes flattened oval in shape and then disc-like. 

 Periclinal divisions yield a dermatogen and a central tissue mass. 

 Later, two cotyledons, a plumule and a radicle are organised, and 

 incipient vascular tissue is differentiated within. Fig. 63a, b (Brough, 

 1933). In Protea lepidocarpon, the embryo also passes through a 

 globular stage like that of Grevillea, and in it also there is no suspensor 

 (Ballantine, 1909). Special interest attaches to the systematic affinity 

 of the Proteaceae. In Engler's arrangement, and also in Rendle's, they 

 are associated with the Santalales; in Hutchinson's with the Thymeh- 

 aceae; and in Balfour's with the Rosales. On the embryological and 

 other data for Grevillea, Brough considers that the simplicity of the 

 Proteaceae may be primitive and, if so, that affinities with an order 

 lower in the scale than the Thymeliaceae would have to be sought. 

 It may here be noted that some features in the embryogeny are of the 

 kind found in primitive families related to the Magnoliaceae. 



MORE ADVANCED DICOTYLEDONS 



In Chapter XIII a considerable number of representative embryonic 

 developments among polypetalous dicotyledons have been illustrated. 

 The aim in this Section is to ascertain if those dicotyledons, which 

 are held to be advanced on the criteria of floral morphology, show 

 embryonic developments which support this view, or otherwise have 

 features of special interest. 



In some primitive dicotyledons, as indicated in the foregoing 

 Section, the suspensor may be relatively inconspicuous, grading into 

 the embryo proper. In other dicotyledons this organ is liable to undergo 

 various modifications. The large ellipsoidal suspensor of Capsella, 

 Fig. 54, has already been noted as being quite exceptional in the 

 Cruciferae; so also is that of Penthorum, Fig. 6I0-Q, among the 

 Saxifragaceae (Lebegue, 1952). Elongated suspensors are common in 

 certain polypetalous families and may be very striking in some 

 Sympetalae. In Salvia splendens the filamentous proembryo elongates 



