CYCADALES 



29 



turgid end of the tube bursts and discharges its contents into the 

 chamber, in whose liquid numerous sperms have been observed 

 swimming. As the archegonium necks open into the bottom of 

 this chamber, the sperms swim to them and pass down to the egg. 

 Webber observed in Zamia as many as four sperms in a single 

 neck. 



As the sperm passes into the cytoplasm of the egg Ikeno and 

 AVebber both observed that the cytoplasmic mantle with its cili- 

 ated band slips off, and is left in the peripheral region of the 

 egg cytoplasm, the sperm nucleus moving alone toward the egg 

 nucleus. Ikeno states that shortly before the entrance of the 

 sperm the egg nucleus develops a cuplike depression, into which 

 the sperm nucleus is re- 

 ceived. In any event, the »^ \ 

 latter imbeds itself in the 

 former, and, according to 

 Webber, remains distinct 

 for a long time (Fig. 

 25). Ikeno claims that 

 the sperm nucleus " dis- 

 solves " within the egg 

 nucleus, and that all nu- 

 clear organization is lost, 

 but it seems more likely 

 that the same condition 

 obtains as in Conifers, a 

 condition which might 

 very easily have escaped 

 observation. 



The prominent devel- 

 opment of the pollen tube 

 as an absorbing organ 

 suggests a question as to 

 its original significance. 

 Associated with ciliated 

 sperms, which have devel- 

 oped in close proximity to the egg, the function of the tube as 

 a sperm carrier is reduced to a minimum, and in fact does not 

 seem to occur in the Cycads. It is an interesting question, 

 therefore, whether the pollen tube originated as an absorbing 



Fia. 25.— Fertilization in Cyeads : A^ fusion of 

 the nuclei in Cyms revoluta, t indicating the 

 so-called trophoplasmic substance ; B, fusion 

 of the nuclei in Zamia integrifoUa, b being 

 the discarded ciliated band, x 20; C, the male 

 nucleus (mn) of Zamia integrifolia after slip- 

 pingiromthe cytoplasmic sheath and ciliated 

 band, x 66.—^, after Ikeno ; B and C, after 

 Webber. 



