April, 1905.] Staphylea trifoliata. 321 



The embryo sac widens slightly as it develops to the eight 

 celled stage (Figs. 11-13) and the nuclei arrange themselves in 

 the normal positions, three at the top becoming the synergidae 

 and egg cell, the three lowest settle into a pocket and gradually 

 disintegrate while the two polar nuclei approach each other and 

 finally come to rest in contact. 



Sections which showed the archesporial cells showed the. 

 microspores fully developed and the tapetal layer already break- 

 ing down (Fig. 14). Older flowers gave thick-walled pollen 

 grains having two nuclei, the pollen tube nucleus and the gen- 

 erative nucleus. This pollen grain (Fig. 15) resembles those of 

 Acer rubrum (Mottier) and Staphylea pinnata (Strasburger) . 

 The latter reports the division of the generative cell into the two 

 sperm cells after the formation of the pollen tube. The gen- 

 erative cell stains quite dark and is apparently enclosed by a 

 wall, making the entire pollen grain very similar to that of the 

 staminate flower of Acer rubrum. 



In the formation of the definitive nucleus two polars usually 

 unite (Fig. 13) but in several instances three exactly similar 

 nuclei were found fusing (Fig. 17). In one case, however, there 

 was found what seems to be the union of one of the sperm nuclei 

 with the polars (Fig. 1(1). This third nucletis is surrounded by a 

 small amount of cytoplasm which stains distinctly darker than 

 that of the polars and the nucleus contains a single small dark 

 nucleolus. 



After fertilization the embryo sac enlarges, the formation of 

 endosperm occurs rapidly and the ovule increases greatly in size. 

 The endosperm forms a large loose single layered lining for the 

 entire embrvo sac before any division of the one celled embryo 

 occurs. The ovules are about one-fourth the mature size before 

 anything larger than a one-celled embryo is found (Fig. IS). 

 The two-celled (Fig. 19), and four-celled stages (Figs. 20,21 and 

 25), were found in half grown ovules. Seeds which were full size 

 but still not too hard to section contained embryos still too 

 young to show the development of the cotyledons (Figs. 22-24). 

 Capsules which contained these full sized ovules had attained 

 their normal bladdery inflation. The endosperm was abundant 

 but the nuclei had not begun the formation of walls so that the 

 multinucleate cells which Strasburger finds in Staphylea pinnata 

 were not observed. 



The synergidae have usually disappeared or are completely 

 obscured by the abundant endosperm before the one celled 

 embr^^o divides but in a few cases traces of them were seen with 

 a four-celled embryo (Fig. 20). No traces of the antipodals 

 were evident after division of the endosperm nuclei became rapid. 

 Division of the suspensor occurs with the formation of the 

 quadrant and seems to retrogress towards the basal cell 





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L I B R A R Y U 



