184 



INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



in plants ordinarily classed as porogamous there are several modi- 

 fications. To mention a few examples, in Acacia (Newman, 1934) 

 the integuments are still below the apex of the nucellus at the time 

 of fertilization so that a micropyle does not exist at this stage and in 

 Philadelphus , Utricularia, Vandellia, and Torenia the embryo sac 



Fig. 108. Course of pollen tube in ovule of Casuarina equisetifolia. A, optical 

 longitudinal section of entire ovary; pollen tube is represented by heavy black 

 line. B, l.s. ovule reconstructed from several sections to show path of pollen tube. 

 (After Swamy, 1948.) 



