Spermatophytes Angiosperms 



277 



invariably show a difference in staining capacity when the male 

 nuclei are just discharged from the pollen tube. With cyanin and 

 erythrosin, the male nucleus stains blue and the female red; hence 

 the obsolete terms cyanophilous and erythrophilous. As the nuclei 

 come into contact within the egg, they begin to stain alike, the male 

 nucleus staining more and more like the female. In the final stages 

 of fusion it is difficult, or 

 impossible, to distinguish 

 the two nuclei. The male 

 nucleus which takes part in 

 the "triple fusion" to form 

 the endosperm nucleus be- 

 haves in the same way. 



Lilium is a very good 

 and always available type 

 for illustrating fertilization 

 (Fig. 100). Take ovaries 

 from flowers whose petals 

 have withered but have not 

 yet fallen off. Though 

 much smaller, Silphium is 

 a good type, because its 

 curved or twisted male nu- 

 clei are easily distinguished 

 from the spherical nuclei 

 in the embryo-sac. The 

 embryo-sacs of orchids are 

 very small, but ovules are 

 extremely numerous and the chances for securing the fusion of nuclei 

 are correspondingly good. In Cypripedium the nuclei do not fuse in 

 the resting condition, but the chromosomes of the two parents are 

 perfectly distinct in the egg. The general statement is that nuclei 

 fuse in the " resting condition." 



The Endosperm. Some of the preparations intended for fertili- 

 zation will be likely to show early stages in the development of 

 endosperm. 



FIG. 100. Lilium philadelphicum: photomi- 

 crograph of section showing fertilization and 

 also the triple fusion; from a preparation and 

 negative by Dr. W. J. G. Land. X585. 



