278 EMBRYOGENESIS IN PLANTS 



The epiblast in Arena and Triticum appears as a small, non- 

 vasculated scale-like leaf situated on the opposite side of the embryo 

 from the scutellum and inserted slightly lower down on the embryonic 

 axis. Similar reduced foliar members and semi-abortive embryonic leaves 

 are known among pteridophytes. If the developmental sequence in the 

 formation of the lateral members was as follows (1) scutellum, (2) 

 epiblast, (3) coleoptile, and (4) first plumular leaf, we should have an 

 approximately normal phyllotactic sequence. But, as judged by their 

 positions on the embryo axis, the epiblast lies below the scutellum. 

 However, when we consider that the epiblast is on the side of the axis 

 remote from the endospermous nutrition, and that the cotyledon, which 

 is initially terminal, comes to occupy a lateral position and quickly grows 

 to large size, thereby causing modifications in the general relationship 

 of parts, it is by no means inconceivable, though proof has still to be 

 obtained, that the epiblast is a second foliar member of very limited 

 growth. 



PARASITES AND SAPROPHYTES 



In view of the differences, sometimes extensive, in the vegetative 

 development of angiospermic parasites and saprophytes, as compared 

 with normal autotrophic species, it is relevant to inquire if these are 

 foreshadowed in the embryogeny. Here it may be noted that although 

 the vegetative development may be greatly modified by an irregular 

 mode of nutrition, the floral morphology is characterised by a certain 

 constancy. Reduced and anomalous embryos are widely scattered 

 through diff'erent orders and families. Not all of these pertain to 

 parasites and saprophytes, but some do. The morphological observa- 

 tions will gain in value as the related physiological-genetical processes 

 are more fully investigated. A number of curious and reduced embryos, 

 e.g. of Rafflesia, Scurrula, Balanophora, Scabiosa, Aeginetia (Oroban- 

 chaceae); Voyria, Voyriella, Cotylanthera and Leiphaimos (Saprophytic 

 Gentianaceae) are illustrated in Figs. 74-78. Some of these have been 

 described briefly by Maheshwari (1950). 



Cuscuta reflexa shows much variation in the relative developments 

 of the embryo and suspensor (Johri and Tiagi, 1952). The embryo sac 

 conforms to the bisporic Allium type, but abnormal embryo sacs may 

 occur. One of the synergids becomes hypertrophied and persists for a 

 long time, usually associated with the swollen suspensor cells ; occasion- 

 ally a synergid may also be fertilised. The zygote and endosperm 

 develop more or less simultaneously, the latter being at first free nuclear 

 but later cellular and finally gelatinous. The zygote divides trans- 

 versely; the basal cell gives rise to the suspensor with some contri- 

 bution from the terminal cell. The suspensor may develop as a series 



