GNETALES 129 



In Gnetum our only knowledge of the male gametophyte 

 comes from the work of Lotsy ^^ upon G. Gnemon, in which the 

 pollen tube just before fertilization was observed to contain the 

 tube nucleus and two male cells of the ordinary Conifer type. 

 Concerning the male gametophyte of Tumboa the only available 

 information is contained in a few figures by Strasburger.* The 

 pollen grain is rather narrowly oblong in section, and on one of 

 the broad sides of the section a small lenticular cell is shown, 

 undoubtedly representing a vegetative cell. Whether there is 

 only a single persistent cell of this kind, as in Cycads, or whether 

 it is but one of two cells, as in Ginkgo and Conifers, is not appar- 

 ent. The figures also show the division of the nucleus of the 

 antheridium initial into tube nucleus and generative nucleus. 

 Such cAddence as is available indicates that the male gameto- 

 phyte conforms to the type observed among other living groups 

 of Gymnosperms. 



FEETILIZATION 



We have no information concerning the fertilization of 

 Ephedra. The anomalous behavior of Tumboa has already been 

 referred to, in which the wall of the archegonial initial develops 

 a tubular process that penetrates the nucellus, meets a de- 

 scending pollen tube, and receives its discharge. The advance 

 of archegonial tubes and pollen tubes is expedited by the numer- 

 ous passageways which riddle the caplike apex of the nucellus. 

 The egg remains in the bulbous basal portion of the archegonial 

 initial, and is fertilized there. 



The fertilization of Gnetum Gnemon is given in consider- 

 able detail by Lotsy.^^ One or more pollen tubes, each con- 

 taining a tube nucleus and two male cells, penetrate into the 

 micropylar chamber of the embryo sac, either at its apex or at 

 the side. The tip of the tube within the sac usually becomes 

 much distended, and discharges both male cells through a ter- 



cells; G, longitudinal section of a mature ovulate flower, showing the "perianth " (p), 

 ■outer integument (o), and inner integument (i), x 33 ; ^, embryo sac with free nuclei in 

 a parietal layer, and showing the beginning of the constriction which results in the 

 antipodal and micropylar chambers ; /, cell formation in the antipodal chamber, another 

 sac which is being pushed aside is shown at the right above, x 50 ; Ji upper portion of 

 sac soon after fertilization, showing a pollen tube with its nucleus {t), oospores (/), and 

 unfertilized eggs, x 340 ; K, embryo sac showing the suspensorlike development of the 

 oospore (g) advancing toward the antipodal endosperm, x 50. — All from Lotsy except- 

 ing F, which is after Stkasbbrqek. 



