THE ANGIOSPERMAE 



1449 



nucleus the male enlarges considerably and its content of nucleic acid dimi- 

 nishes, as in the oosphere nucleus, to such an extent that it gives hardly any 

 stain with the Feulgen reagent. Nuclear fusion seems to be an amalgama- 

 tion. There is no opening of the female nuclear membrane, nor has solu- 

 tion been observed (Fig. 1331)- The nuclear membrane of the male 



B 



H 



Fig. 1 33 1. — Impatiens ghuuiidigeya. Entry of male nucleus into the female. A, Two nuclei 

 in external contact. B, D and E, Solution of the contact membrane and entry of the male 

 nucleus. C, F, G and J, Appearance of the male nucleolus and its union with that of the 

 oosphere. B-J, Increasing chromatin content of the fertilized nucleus. J shows the 

 prophase chromosomes of the first division of the zvgote. D, A case of dispermv. 

 {After Steffen.) 



has been seen after entry into the primary endosperm nucleus (Fig. 1332), 

 though not in the oosphere. It must rapidly disappear, and the contents 

 of the male nucleus disperse within the female. The sperm nucleus does 

 not always possess a nucleolus, but at the time of fusion it appears, or 

 reappears, at first as a minute granule, which rapidly enlarges, then moves 

 towards and fuses with the female nucleolus. Nuclear fusion is a relatively 

 slow process and may take several hours to complete from the time of first 

 contact, but the data are very scanty. 



Immediately after fusion the nucleic acid content ot the fusion nucleus 

 rapidly increases and the structure of prophase chromosomes re-emerges, in 

 other words, the fusion nucleus retraces the changes which took place during 

 the maturation of the oosphere nucleus, and the duration of the process 

 causes a certain delay before the first zygote division. In the endosperm 

 cell the recovery process is quicker, hence it is usually the first to divide, in 

 fact it may divide several times before the fertilization of the oosphere is 

 completed. Some aberrations of the normal fertilization process will be 



