THE ENDOSPERM 



223 



observed to be larger than those in the micropylar part. 4 This may 

 be due to an actual growth in their size as in Colutea (Nemec, 1910), 

 Ranunculus (Schurhoff, 1915), and some members of the Cistaceae 

 (Chiamgi, 1925), or to a fusion of adjacent nuclei as in Primula 



ABC D E 



Fig. 120. Endosperm in orchids. A, Corallorhiza maculata, six-nucleate embryo 

 sac; micropylar polar nucleus has migrated to the base of the sac. B, a stage in 

 fertilization, showing one male nucleus fusing with the egg nucleus and the second 

 male nucleus still in micropylar part of embryo sac. C, embryo sac, showing the 

 young proembryo and the second male nucleus fusing with the other free nuclei in 

 sac. D, Bletia shepherdii, young proembryo and triple fusion nucleus. E, same, 

 later stage of proembryo accompanied by degeneration of endosperm nucleus. 

 (After Sharp, 1912.) 



(Dahlgren, 1916), Tilia (Stenar, 1925), Mains (Wanscher, 1939), 

 and some members of the Compositae (Poddubnaja-Arnoldi, 1931). 5 

 An especially interesting case of an increase in size of the endo- 

 sperm nuclei has recently been described in Echinocystis macrocarpu 



i Rarely, as in Fagraca (Mohrbutter, 1936), the reverse happens and the micro- 

 pylar nuclei are the larger. 



5 Although fusions may take place during the free nuclear stage, they are more 

 abundant after wall formation has taken place and the endosperm has become 

 chambered into several multinucleate protoplasts. 



