Fertilization in Pinus Strobus . 455 
fertilization in plants consists in the fusion of two nuclei to 
form a resting nucleus. 
Students of Pinus , however, have attained quite different 
results, and find, in this genus, phenomena very similar to 
those occurring during fertilization in some animals. Black- 
man concludes that in Pinus sylvestris ‘ no resting fertilized 
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 spirems were formed 
in Pinus Laricio , but, as so many stages were lacking in his 
material, he hesitated to draw definite conclusions. As a 
result of the present studies, it is found that, in Pinus 
Strobus , the chromatic portions of the sexual nuclei remain 
distinct until the daughter-nuclei are formed ; and there is 
never any true fusion of the conjugating nuclei ; i.e. the two 
nuclei do not form one individual enclosed by a definite 
membrane. 
No centrosome or centrosome-like body has been observed 
in connexion 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 the force initiating and 
controlling the division is supplied by the sperm- and not by 
the egg-nucleus — this force manifesting itself only in the 
presence of the egg-cytoplasm. 
The Division of the two Segmentation-Nuclei. 
The two daughter-nuclei remain in the upper part of the 
egg and pass through the same stages in their development 
as those described in the maturation of the egg-nucleus, 
except that, as a rule, no nucleolus becomes apparent within 
them. These nuclei have been observed to approximate in 
Thomas (’00) in Caltha , Wager (’00) in Peronospora , and Wuicizki (’99) 
(according to Arnoldi and to reviews in the Bot. Zeit. and in the Journ. Roy. 
Micr. Soc.) in Larix. 
