280 



EMBRYOGENESIS IN PLANTS 



coiled embryo, with a distal apex, small plumular scales, and a feebly 

 differentiated central vascular strand. There are no cotyledons. In 

 other species of Cuscuta the embryogeny is generally comparable 

 (Fedortshuk, 1931; Tiagi, 1951). Johri and Tiagi disagree with 

 Johansen's placing of the Cuscuta embryo in his Caryophyllad type; 



eXgAa 



pt A 



B 



Fig. 75. Embryogeny in Cuscuta reflexa 



A, Three-celled proembryo, with free endosperm nuclei; .?, haustorial synergid; pt, 

 pollen tube. B, An older embryo ; the basal region of the proembryo has developed 

 into two large vesicular, coenocytic suspensor cells, b and c; the distal region has 

 given rise to four tiers. C, A yet older stage, showing the distal embryonal mass. 

 D, Proembryo with reduced vesicular suspensor; s, synergid; E, Proembryo with- 

 out vesicular suspensor. F, G, Maturation of coiled embryo; .s7, shoot apex; ps, 

 plumular scale; r, root; vs, vascular strand. (A-E, X 165; F, G, x 4; after 



Johri and Tiagi.) 



they consider that it properly belongs to the Solanad type. Tiagi (1951) 

 has compared the embryological development of Cuscuta with that in 

 non-parasitic species of Convolvulaceae, and considers that it should 

 be removed to a separate family (i.e. the Cuscutaceae), thus supporting 

 a view already advanced by taxonomists. In the genus Cuscuta the 

 genetical changes associated with the transition to the parasitic mode 

 of life can be detected in various anomalous developments of the 

 embryo. 



