460 THE AMERICAN NATURALIST. (VoL. XXXIX. 
ing chief events and principles of fertilization. Thus Van 
Beneden's conclusion of 1883 that sexual nuclei are equivalent 
in their chromatin content at the time of fusion irrespective of 
differences in size is admirably borne out by Miss Ferguson's 
(: 04) studies on the pine. In this form as in the gymnosperms 
generally the male nucleus is much smaller than the female and 
comes to lie in a depression in the latter before the actual fusion 
takes place. Afterthe fusion the paternal and maternal chromo- 
somes are found in two groups side by side preparatory to the 
first cleavage mitosis and are indistinguishable except for their 
position ; the chromatin of the two sexes is equal in amount as 
far as can be seen. Then the observations of the Hertwig 
brothers, in 1887, and Boveri, in 1889 and 1895, that the sperm 
nucleus could enter and cause the development of denucleated 
eggs or their fragments thus taking the part of a female nucleus 
in parthenogenesis, were established for plants by Winkler's 
(: OI) experiments on Cystoseira. Winkler was able to divide 
the egg of this brown alga into a nucleated and a non-nucleated 
portion and he found that sperms entered the non-nucleated 
parts and caused them to develop sporelings side by side with the 
fertilized nucleated portions. The sporelings from the non-nucle- 
ated fragments, controlled by the sperm nuclei alone, developed 
about half as rapidly as those from the originally nucleated por- 
tions which of course were dominated by sexually formed fusion 
nuclei, but the two sets of sporelings were alike in form as far as 
they were grown. Only with respect to Boveri's celebrated 
theory that the sperm brings to the egg in the centrosome the 
mechanism of cell division, do plants fail to support the conclu- 
sions of certain zoölogists with respect to the most important 
events of fertilization. This point upon which zoólogists are 
not in full accord will be discussed later. There is general 
agreement in the view that the male nucleus of plants supplies 
chromosomes equal in number and equivalent quantitatively to 
the female, and general accord in the conclusions that the chro- 
mosomes by their individuality, apparent permanence of struc- 
ture, and fixed behavior must be bearers of hereditary characters. 
Evidence from the most recent investigations upon favorable 
forms of both animals and plants indicates that the chromosomes 
