No. 460.] STUDIES ON PLANT CELL. V. 233 



about equal size whose chromatin contents unite in a fusion 

 nucleus to form a common network in which male and female 

 elements cannot be distinguished. A similar condition obtains 

 in Cryptomeria, according to Lawson (:O4b), where a fusion 

 nucleus is described in which paternal and maternal chromatin 

 are mingled together in a nucleus that passes through a short 

 period of rest before the development of the first cleavage 

 spindle. In view of the work on Pinus I think it may safely be 

 questioned whether in Sequoia and Cryptomeria the maternal 

 and paternal chromatin really does form a common network in 

 the resting fusion nucleus. The subject is one very difficult of 

 study and demands more stages than Lawson seems to have 

 followed. 



Fertilization in the cycads is not as completely known as for 

 the conifers. Webber (:oi) figures the sperm nucleus of 

 Zamia imbedded in the egg nucleus but quite distinct from it as 

 in the pine but the further history leading to the development 

 of the first segmentation spindle was not followed. On the 

 other hand Ikeno ('98b) described in Cycas the formation of a 

 cup-like depression in the egg nucleus to receive the sperm 

 nucleus which was said to enter and fuse completely with the 

 female and the same author (Ikeno, :oi) reports a complete 

 fusion of the gamete nuclei in Ginkgo and did not distinguish 

 the paternal and maternal chromosomes during the formation of 

 the first segmentation spindle. However it is probable that 

 more detailed studies among the cycads and in Ginkgo will 

 show a behavior of the sperm nucleus together with the pater- 

 nal and maternal chromatin essentially similar to that of the 

 conifers. All investigations among the cycads and in Ginkgo 

 agree that cytoplasmic structures of the sperm (blepharoplasts, 

 cilia, etc.) are left behind in the cytoplasm of the egg before the 

 gamete nuclei unite. 



Our knowledge of the details of fertilization in the angio- 

 sperms is surprisingly meager. The only account of the chro- 

 matin is that of Mottier ('98 ; : O4b, p. 176) for Lilium. He 

 describes and figures the two gamete nuclei as uniting with 

 their chromatin in the resting condition. The nuclear mem- 

 branes disappear at the surface of contact and the two nuclei 



