. Morphology of spermatophytes. [Part I. Gymnosperms]. Gymnosperms; Plant morphology. 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
. Morphology of spermatophytes. [Part I. Gymnosperms]. Gymnosperms; Plant morphology. 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 repres
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