GNETALES 4°^ 



way, and contains one of the free nuclei, with which numerous 

 starch grains are associated. In this terminal embryo cell free 

 nuclear division continues, accompanied by cleavage walls, until 

 a multicellular embryo is formed (figs. 457, 458). The formation of 

 cleavage walls appears to continue until uninucleate cells are produced. 



As in the case of Welwitschia, it had been supposed that in the 

 embryo-formation of Gnetum the preliminary stage of free nuclear 

 division, common to other gymnosperms, had been eliminated, and 

 that the first nuclear division was accompanied by wall-formation, as 

 in angiosperms. In Onetum Gnemon, however, free nuclear division 

 not only characterizes the proembryo, but also the early stages of 

 the embryo. In comparing Gnetum with Ephedra it will be seen 

 that the number of free nuclei formed by the egg in each case is approx- 

 imately the same, the difference being that in Ephedra several sus- 

 pensors are formed by independent proembryonal cells, while in 

 Gnetum a single suspensor is formed by the fertilized egg. 



The later stages of the embryo of Gnetum Gnemon have been 

 described by Bower (8), the basal cells of the embryo group produ- 

 cing embryonal tubes, as in Welwitschia; and the young seedling 

 showing the same endospermic foot (rodlike) attached between the 

 long hypocotyl (bearing two small cotyledons) and the root. Hill 

 (26) has studied the germination of these species, and reports that 

 the hypocotyl soon escapes from the seed coats, leaving behind a 

 foot or sucker in close connection with the storage tissue. The coty- 

 ledons are at first small, but later enlarge somewhat and do photo- 

 synthetic work; and the rodlike foot in the center of the endosperm 

 contains vascular tissue. This foot, reported for Gnetum and Wel- 

 witschia, needs investigation, for there is no such structure in Ephedra, 

 the only genus of the Gnetales whose germination we have seen. 

 In that genus the germination is as in Pinus, the cotyledons being 

 pulled out of the testa and spreading, and there is left no structure 

 imbedded in the endosperm. Whether this sucker-like outgrowth 

 from the cotyledonary node of Gnetum and Welwitschia is to be 

 regarded as a "foot," with all the morphological connections that 

 that term imphes, or merely a special "peg" such as appears in cer- 

 tain dicotyledons, is a question to be decided only by one's point 

 of view. 



