EMBRYOGENESIS IN FLOWERING PLANTS 



285 



branches which penetrate the integument (Tiagi, 1952). In Cistanche 

 tubulosa (Orobanchaceae), a leafless total parasite, growing on the 

 roots of Acacia and other trees, Tiagi (1952) found that the embryo sac 

 is not characterised by any unusual features, but after fertilisation the 

 embryo remains small and relatively undeveloped. In the small mature 

 seed the embryo is an ovoid structure with tissue diff'erentiation but 



Fig. 78 



A, B, Embryogeny in Monotropa hypopitys. A, L.s. of seed, showing embryo- 

 germling, as yet without mycorrhizic fungus. B, An older germhng with fungus 

 (B, X 10; after Francke). C-E, Embryogeny in Zeuxine sulcata. C, Binucleate 

 embryo sac and two-ceiled nucellar embryo. D, E, Formation of several embryos 

 (C, X 490; D, E, x 56; after Swamy). 



without differentiation of plumule, cotyledons or radicle. The cellular 

 endosperm forms a rather feeble chalazal haustorium but a very 

 aggressive micropylar one with intercellular hypha-like branches which 

 penetrate the integument. These endosperm developments, however, 

 are general in the autotrophic Scrophulariaceae and are not correlated 

 with the parasitic habit in Cistanche. 



In Monotropa hypopitys (Ericales: Monotropaceae), a saprophytic 

 species well known because of its ectotrophic mycorrhizic nutrition, the 

 mature seed is very small and contains an embryo consisting of three 

 cells only, surrounded by an endosperm of nine cells, Fig. 78a, b. 

 During germination, which apparently only takes place after some 



