1919] EVANS— PENTSTEMON 437 



EXPLANATION OF PLATE XII 



All the drawings were made at table level with the aid of an Abbe camera 

 lucida. The labels are: a, sperm; b, polar fusion nucleus; c, megaspore; 

 d, micropylar end of embryo sac; e, embryo; h, haustorium; s, starch; 

 /, tapetum. 



Fig. I. — Synapsis in the megaspore mother-cell; X880. 



Fig. 2. — Row of 4 megaspores showing fourth developing into embryo 

 sac; X880. 



Fig. 3. — Row- of 4 megaspores showing third developing into embryo sac; 

 X880. 



Fig. 4. — An 8-nucleate embryo sac before maturity, showing character- 

 istic shape of sac and egg apparatus beginning to form; X880. 



Fig. 5. — ^Micropylar end of mature embr>'o sac showing egg apparatus well 

 formed and migration of polar fusion nuclei; X460. 



Fig. 6. — IMicropylar end of mature embryo sac showing egg apparatus, 

 entrance of pollen tube, 2 sperms, polar fusion, and starch; X880. 



Fig. 7. — Mature embr>'o sac showing double fertilization; X880. 



Fig. 8. — Stage showing growth of suspensor pushing young embryo between 

 micropylar haustoria w-hich have already begun to disintegrate; section a little 

 to one side of chalazal haustorium; tapetum present; X460. 



Fig. 9. — Stage showing binucleate chalazal haustorium; X880. 



Fig. 10. — Late stage of endosperm formation showing embryo imbedded; 

 micropylar end of sac already beginning to collapse; X460. 



