No. 460.] STUDIES ON PLANT CELL.— Vi 255 



nomena does not become less by this treatment which certainly 

 avoids much confusion of expression. 



There is left for consideration one other group of nuclear 

 fusions which may have sexual significance although such is 

 not obvious, namely the fusions of polar nuclei in the embryo 

 sac of angiosperms and the triple unions of the above with a 

 second sperm nucleus which is often called "double fertiliza- 

 tion." Several excellent reviews of this subject have appeared, 

 notably by Strasburger (:00b), Sargant (:oo), Coulter and 

 Chamberlain (: 03), Mottier (: 04a, b), and Gu6rin (: 04). The 

 explanation of this phenomenon is likely to rest finally upon 

 morphological analysis but at present we are uncertain of the 

 homologies of the polar nuclei and the part they play in the 

 evolutionary history of the endosperm. The most striking 

 theory of the endosperm was proposed by LeMonnier ('87) who 

 suggested that the fusion of the polar nuclei gave origin to a 

 second embryo modified to nourish the normal embryo. One 

 of the polar nuclei is always closely related to the s.gg nucleus 

 so that in the triple fusions (the sperm with two polar nuclei) 

 we have conditions very close to normal fertilization, the dis- 

 cordant element being not the sperm nucleus but the antipodal 

 polar nucleus. The triple fusions would seem at first thought 

 to be rather favorable to LeMonnier's theory although it is plain 

 that with such a diverse mixture of chromatin from three nuclei 

 the resultant structure can scarcely be called a sporophyte 

 embryo from the very grotesqueness of its make-up. Miss 

 Sargant considers the fusion of the second sperm with the 

 ihicropylar nucleus as sexual in character but so complicated 

 by the introduction of the antipodal polar nucleus that the 

 result is a bizarre structure not strictly comparable to a normal 

 embryo. In the final solution of this problem we must know 

 whether in phylogeny the sperm and micropylar polar nucleus 

 fused first and the antipodal entered into the process later or 

 whether the polar nuclei began the habit and the second sperm 

 nucleus was drawn afterwards into the activities. Should the 

 first possibility be established the sexual nature of the process 

 would seem clear while in the second the events would be of 

 the nature of asexual nuclear fusions. While we know very Uttle 



