282 EMBRYOGENESIS IN PLANTS 



In Striga lutea, a semiparasitic species of the Rhinantheae-Gerar- 

 diae (Scrophulariaceae), the proembryo has large 'tuberous haustoria' 

 at the base of the suspensor, but otherwise it shows no abnormal 

 features, the mature embryo being a typical dicotyledonous one. The 

 chalazal end of the cellular endosperm develops into a long binucleate 

 haustorium which penetrates the integument; the micropylar hausto- 

 rium is inconspicuous. The question as to whether the parasitic mode 

 of life of the plant affects the embryo sac and embryonic development 

 is one which has often been raised (Bernard, 1903; Mitchell, 1915, etc.). 

 The evidence indicates that there is no direct relationship between the 

 habit of the plant and the haustorial developments of the endosperm. 

 These structures are a general feature in the Scrophulariaceae and are 

 in no way restricted to the parasitic and semi-parasitic genera and 

 species. Thus, in the holoautotrophic genus Veronica, the endosperm 

 haustorial development is as in the Rhinantheae. In studies of four 

 total parasites, namely, Lathraea, Orobanche, Phelipaea, and Cytinus, 

 Bernard (1903) found all stages of haustorial development. Lathraea 

 showed the most extensive haustorial development. Also, in the 

 production of fertile seeds, the parasitic members appear to be just as 

 successful as their autotrophic near-relatives. In other words, the 

 genetical changes which have led to the saprophytic, semi-parasitic, or 

 parasitic modes of life in these organisms have not materially affected 

 the mechanisms of reproduction and embryogenesis. The embryonic 

 development in Orobauche cernua, Fig. 77, is characteristic of the group. 



In Aeginetia indica (Orobanchaceae), a small parasite on grass roots, 

 the ovules are very small, the nucellar epidermis degenerates, and an 

 inconspicuous integumentary tapetum surrounds the mature embryo 

 sac. The early embryogeny is fairly normal, but the mature embryo 

 consists simply of an ellipsoidal cellular mass, with the remains of the 

 suspensor at one end, embedded in a cellular endosperm. The endo- 

 sperm gives rise to a small chalazal haustorium and to an aggressive 

 micropylar haustorium. The latter develops intercellular hypha-like 



Fig. 76. Embryogeny in Loranthaceae 



A-F, Embryogeny in Dcndropthocfalcata. A, B, C, Basal, middle and upper regions 

 of a gynoecium in longitudinal section. D, Entire flower; the egg apparatus in the 

 several elongated embryo sacs can be seen in the style; the antipodal cells are in 

 contiguity with the collenchymatous pad {col) just above the base of the ovary. E, 

 L.s. of style, showing the biseriate proembryo. F, L.s. of fruit; c«, calycalus; e, em- 

 bryo; cm/, endosperm ; po, zone of parenchyma; />.?, perianth scar; /, leathery coat 

 of fruit wall; s, space through which the embryo sacs pass into the ovary; ss, scar 

 of style; //>, vascular zone; r.v, viscid layer (E, x 130; all after Bahadur Singh). 

 G, H, Embryogeny in Titpeia antarciica. G, L.s. of female flower, showing elon- 

 gated embryo sacs with egg apparatus (£) in the style, and collenchyma sheath (c) 

 at the base. H, L.s. of developing fruit, with viscous tissue (V), stylar disc (D), 

 collenchyma sheath (C), embryo (£). (G, x 25; H, x 30; after Smart). 



