. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. LOXSOMACEAE 573 The receptacle performs an important part in connection with dispersal. At first it is short, so that the sporangia are all included within the indusium (Fig- 32° E)> and this is so till the oldest sporangia are mature; an inter- calary growth then takes place at the base of the receptacle, the thin- walled cells above the terminal mass of tracheids (tr.) become greatly â¢elongated (Fig. 320 a), forming a sort of pseudopodium (ps.), upon which the sporangia are raised so as to proj
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. LOXSOMACEAE 573 The receptacle performs an important part in connection with dispersal. At first it is short, so that the sporangia are all included within the indusium (Fig- 32° E)> and this is so till the oldest sporangia are mature; an inter- calary growth then takes place at the base of the receptacle, the thin- walled cells above the terminal mass of tracheids (tr.) become greatly â¢elongated (Fig. 320 a), forming a sort of pseudopodium (ps.), upon which the sporangia are raised so as to project beyond the lip of the protective indusium, and are thus free to scatter their spores. The arrangement is similar to that seen in the Hymenophyllaceae, but in Loxsoma the pseudo- podium is formed independently of the long-continued formation of a series of sporangia. The sporangium makes its first appearance as a massive deeply sunk cell, near the base of the groove between the receptacle (r) and the indusium (ind.) (Fig. 320 b): the first segmentation in it passes down to the base of the cell, as in the Schizaeaceae and some other Simplices; the later ones cut the previous wall obliquely, and thus a three-angled conical cell is surrounded by three lateral segments. The cap-division, and segmentations forming the tapetum take place in the usual way; the inner series of tapetal cells enlarge considerably, and become polynucleate, thus resembling other large sporangial types. The definite sporogenous group is â¢composed of 16 spore-mother-cells, which undergo a tetrad division to give typically 64 large spores. The chief point of anatomical interest is the structure of the stele of the stem : a transverse section of an internode shows a typical solenostele, with phloem, pericycle, and endodermis, both outside C^Z\. --It. and inside of the continu- ous ring of xylem. The protoxylem elements are all â¢scalariform, and are not localised into groups, but are dist
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