126 



MORPHOLOGY OF SPERMATOPHYTES 



gonia, and Gnetum, with its free eggs. No less remarkable than 

 the structure of the archegonium, if such it may be called, is its 

 behavior in connection with fertilization. It is reported that 

 each archegonial cell develops a long tubular process which 

 penetrates into the sterile tissue of the nucellus, and passing 

 along one of the numerous passageways of the beak meets the 

 approaching pollen tube (Fig. 90). It is needless to comment 



upon this peculiar structure and be- 

 havior until the details are more fully 

 known. 



Gnetum. — In Strasburger's ac- 

 count ^ of G. Gnemon it is not apparent 

 whether or not the mother cells de- 

 velop a row of potential megaspores. 

 In any event, several megaspores begin 

 to enlarge, and free nuclear division 

 may occur in a number of them before 

 one finally dominates the rest. 



The germination of the megaspore 

 has been given in detail by Lotsy,^^ and 

 his account for Gnetum Gnemon is as 

 follows: The nucleus of the megaspore 

 begins the usual series of free nuclear 

 divisions, but since there is such great 

 diversity between the micropylar and 

 antipodal contents of the embryo sac, 

 Lotsy raises the question whether the 

 polarity of the sac may not have been 

 established by the first division of the 

 megaspore nucleus. Unfortunately, 

 the persistent absence of spindles in 

 his material prevented him from an- 

 swering the question. Soon the free 

 nuclei become imbedded in a thin parietal layer of cytoplasm 

 surrounding a great central vacuole (Fig. Ql, H). In this con- 

 dition a constriction develops in the sac somewhat below the mid- 

 dle of its long axis, which persists until the final growth of the sac 

 obliterates it. This constriction divides the sac into two very dis- 

 tinct chambers. The smaller antipodal chamber speedily fills 

 with a compact tissue, in the way usual for the whole embryo 



Fig. 90. — Tumhoa: the figure 

 to the right represents a 

 group of arohegonium ini- 

 tials sending out tubular 

 prolongations into the nu- 

 cellus to meet the descend- 

 ing pollen tubes ; the figure 

 to the left and above rep- 

 resents the suspensorlike 

 elongation of the oospore, 

 bearing at its tip embry- 

 onal cells. — After Stkab- 



BUEGEB. 



