164 BOTANICAL GAZETTE |march 



of centrosome without being genetically connected with that 

 structure. 



In Nephrodium there is present no centrosome in the whole life- 

 history, and the blepharoplasts which arise de novo in the cytoplasm 

 of the spermatid mother cell do not play the part of a centrosome. 

 Since centrosomes are not found in this form it is impossible of course 

 to discuss any relationship between them. If any genetic relation- 

 ship really exists between the two structures in the plant kingdom, 

 evidence might be sought in some of the lower forms, such as Sphace- 

 laria and some other species in Phaeophyceae, in which centrosomes 

 are known and motile spores are produced. 



Fusion of male and female nuclei.— The condition of sexual nuclei 

 at the time of fertilization has been studied in numerous forms of 

 different groups of plants. 



Among thallophytes the fusion of gamete nuclei was observed in 

 Closterium and Cosmarium (Klebahn 52), Rhopalodia (Klebahn 

 54), Cocconeis (Karsten 50), Sphaeroplea (Klebahn 55; Golen- 

 kin 30), Oedogonium (Klebahn 52), Vaucheria (Oltmanns 70; 

 Davis 23), Coleochaete (Oltmanns 71), Fucus (Farmer and Wil- 

 liams 25, 26; Strasburger 86), Dictyota (Williams 97), Batracho- 

 spermum (Schmidle 76; Osterhout 72), Nemalion (Wolfe 

 98), Polysiphonia (Yamanouchi 100), Basidiobolus (Fairchild 27), 

 Albugo (Wager 92; Stevens 81, 82; Davis 22), Peronospora 

 (Wager 93), Pythium (Miyake 63; Trow 91), Achyla (Trow 91), 

 Araiospora (King 51), Sphaerotheca (Harper 34), Pyronema (Har- 

 per 35). No matter whether a condition of heterogamy is established 

 or not in these forms after the union of gametes or gametangia, the 

 male nucleus or nuclei pass into the cytoplasm of the egg or oogonium 

 and union takes place between the male and female nuclei in the 

 resting condition. 



Similar conditions regarding the union of the sexual nuclei in 

 angiosperms were described by Strasburger (84) for Monotropa, 

 by Schaffner (75) for Sagittaria, by Coulter (19, 20) for Lilium 

 and Ranunculus, by Mottier (66, 67) for Lilium, by Land (57) 

 for Silphium, and by others. Mottier gives the most detailed account 

 of chromatin at the time of the union, and figures the gamete nuclei 

 as uniting with their chromatin in the resting condition. In the forms 



