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. After the 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 zoologists with respect to the most important 

 events of fertilization. This point upon which zoologists 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 



