LIFE HISTORY OF PINUS 121 



in plants consists in the fusion of the two nuclei to form a rest- 

 ing nucleus not demonstrably different, except in some cases in 

 its greater size, from the original egg-nucleus. 



Students of certain of the Abietinece^ however, have attained 

 quite different results, and find in these plants phenomena very- 

 similar to those occurring during fertilization in some animals. 

 Blackman concludes that in Pinus sylvestris *' no resting fertil- 

 ized nucleus is ever formed " and that " the half-chromosomes 

 derived from the male and female nuclei respectively, fuse 

 together at the poles of the first segmentation spindle " ; and 

 Chamberlain found that two chromatic spiremes were formed in 

 Pinus Lciricio, but, as so many stages were lacking in his 

 material, he hesitated to draw definite conclusions ; Woycicki 

 ('99) reported a complete fusion of the sexual nuclei in La7'ix^ 

 but in some cases he saw two chromatin-groups, and suggested 

 that they might have been derived, one from each parent ; and 

 Murrill ('oo) has recently described the formation of two distinct 

 spiremes in Tsuga. As a result of the present studies, it has 

 been shown conclusively, as stated by the writer in 1901^'''°'^^, 

 that the chromatic portions of the sexual nuclei remain distinct 

 until the daughter-nuclei are formed ; and there is, moreover, 

 never any true fusion of the conjugating nuclei, that is, the two 

 nuclei do not form one individual enclosed by a definite 

 membrane. 



It is evident from the foregoing, that fertilization in Pinus 

 consists in the complete union of two cells. Cytoplasm fuses 

 with cytoplasm and nucleus unites with nucleus. 



No centrosome or centrosome-like body has been observed in 

 connection with the sexual nuclei, either before or during this 

 division. Although the centrosome as an organ has failed to 

 be demonstrated, yet a detailed study of this mitosis makes the 

 conclusion inevitable that ih.Q /"orce initiating and controlling 

 the division is supplied by the sperm- and not by the egg-nucleus 



ium ; Mottier ('98) in Lilium and ('00) in Dictyota; Nawaschin ('99) in L,iltum, 

 and ('00) in Heliatit/ius, Delphinium and Rudbeckia ; Osterhaut ('oo) in Batra- 

 chosperntum ; Sh.a.vf ('98) in Onoclea; Thorn ('99) va. Adiantum and Aspidium j 

 Thomas ('00) in Caltka ; Wager ('00) in Peronospora ; Webber ('01) in Zamia; 

 all who have described coiled sperm-nuclei ; and all writers with the exception 

 of Ikeda who have published on fertilization in plants during 1902 and 1903. 

 Proc. Wash. Acad. Sci., August, 1904. 



