224 MAINE AGRICULTURAL EXPERIMENT STATION. 



but even the two asexual nuclei also. These nuclei persist for a 

 considerable time, and are to be found in the protoplasm of the 

 cosphere after its nucleus has divided several times." As before 

 stated, however, only one of the male nuclei fuses with the 

 female. 



It is possible, as has been suggested, that the provision of 

 two sexual nuclei is a condition handed down from the time 

 when pollen-tubes normally branched, and there was a proba- 

 bility of two branches reaching different oospheres. In Cupres- 

 sinege, according to Vines,* "one pollen-tube serves for the fertili- 

 zation of several female organs ; consequently several male 

 gametes are produced, the first division of the generative nucleus 

 in the pollen-tube is followed by an aggregation of protoplasm 

 around each of the two new nuclei, so that two primordial cells 

 are formed. Nucleus division is repeated in the primordial cell 

 nearest the apex of the pollen-tube, without any corresponding 

 cell formation, so that several nuclei are to be found in the 

 dilated apex of the pollen-tube ; these, with a certain amount of 

 protoplasm, escape as gametes, and each fertilizes the oosphere 

 of an archegonium." 



At the time of fertilization the pollen-tube is perforated by a 

 aistinct pit or perforation, first described by Hofmeister,t and 

 later by Strasburger.t The same phenomenon has been shown 

 to exist in certain of the Angiosperms, notably, Gnetiun Rtini- 

 phianum and G. ovalifolium.^ Just before fertilization occurs, 

 radial striae extend from the nucleus of the oosphere into the 

 surrounding protoplasm ; likewise from the male nucleus, this 

 phenomenon apparently preceding the re-adjustment of the 

 centrosomes in each case. Then, when the sexual pro-nuclei 

 unite, the new centrosomes formed lie in a plane perpendicular 

 to the longitudinal axis of the archegonium ; the first division of 

 the oosphere occurring in a horizontal plane. 



On the Method of Entering the Nncellus. — One point of inter- 

 est in connection with the passage of the male element, is the 



* Vines, S. H. : Physiology of plants, 616 (1886). 

 fHofmeister: Pring. Jahrb. f. Wiss. Bot., Bel. 1, p. 71. 

 j Strasburger : Bef. bei den Coniferen, pp. 11-14 (18S9j. 



§Kar.sten: Cohn's Beitrage zur Biologic tier PHanzen, Bd. VI, Heft 3, p. 367. 

 Cited by Dixon, o]}. cit. 



