II 



1907] PACE— FERTILIZATION IN CYPRIPEDIUM 369 



of the synaptic knot may be due to gravity. This does not seem to 

 be true in Cypripedium, for the knot was found at all possible posi- 

 tions next the nuclear membrane in serial sections of the same ovary, 

 and even in the same section. This was not only true for cross-sections, 

 but also for longitudinal sections in which, since the ovary stands 

 erect, gravity effects ought to be apparent. Burlingame (6a) has 

 reached this same conclusion in his study of Ophioglossum. 



SUMMARY 



um 



not appearing in the second division^ even in the rare instances in 

 which the nuclei of both daughter cells divide. Two megaspore 

 nuclei are used in forming the embryo sac, the LiHum type using four, 

 and most angiosperms only one. The two megaspore nuclei in the 

 sac of Cypripedium and the four in that of Lilium may be related to 

 double fertihzation. 



2. Cypripedium has only four nuclei in the completed embryo 

 sac. The LiHum type and Cypripedium have the fewest divisions 

 from mother cell to egg reported among angiosperms. A comparison 

 with the animal egg shows only one more division from the mother 

 cell to the egg in Lilium and in Cypripedium than in the maturation 

 of the animal egg. 



3- So-called double fertilization is probably constant in Cypripe- 

 dium. The primary endosperm nucleus (triple-fusion nucleus) is 

 formed by the fusion of the polar, one s}'nergid, and one niale nucleus. 

 Endosperm of four nuclei was found and the probability of other 

 divisions taking place "was noted. 



4- In the presynaptic nucleus there is an evident pairing of the 

 threads, probably of paternal and maternal origin. The gameto- 

 phne number of chromosomes is eleven, the sporophyte number is 

 twenty-two, and the endosperm number is probably thirty-three. 

 Distinct spirems were often found in all fusing nuclei, forming in one 

 instance before contact. From these examples, the possibility of 

 two spirems always forming in the sporophyte nucleus is suggested ; 

 this would secure the independence of the chromatin, and the fusing 

 in s}Tiapsis would permit whatever exchange and mingling of parts 

 there may be^ 



