. Un manuel de botanique pour les collèges et universités ... La botanique. Les PTÉRIDOPHYTES 169 racine, tandis que l'intérieur deux quadrants (dorsal) dirigée développer la tige et la feuille, que Pierce à travers le tissu du thalle sus-jacente (fig. 394). Des enquêtes récentes indiquent cependant que les deux la partie extérieure (ventrale) quadrants peuvent développer le pied, l'intérieur deux-(dorsale) quad- rants formant un tissu qui donne naissance à des feuilles, de la tige et de la racine. Cette méthode de développement suggère que de l'embryon de Ophioglossales, avec laquelle le groupe Marattiaceae semblent être étroitement alliés. Parmi les premiers Polypodiaceae divi

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. A textbook of botany for colleges and universities ... Botany. PTERIDOPHYTES 169 root, while the two inner (dorsally directed) quadrants develop the stem and leaf, which pierce through the tissue of the overlying thallus (fig. 394). Recent investigations, however, indicate that both the outer (ventral) quadrants may develop the foot, the two inner-(dorsal) quad- rants forming a tissue that gives rise to leaf, stem, and root. This method of development suggests that of the embryo of Ophioglossales, with which group the Marattiaceae seem to be closely allied. Among Polypodiaceae the first divi- sion of the egg is parallel with the long axis of the archegonium (fig. 395), the shoot cell being directed towards the apex (notch) of the pro- thallium. At the quadrant stage (fig. 395) the two apically directed quad-. Fics. 394, , 395. — Diagram of quad- rant stage of embryo: 394, Marattia, in which the first wall is transverse to the rants give nse to stem and leaf (the io„g ^xis of the archegonium, the shaded quadrants giving rise to stem and leaf; 395, a polypod, in which the first wall is parallel with the long axis of the archegonium, the shaded quad- rants (directed towards the notch) giv- ing rise to stem (upper quadrant) and leaf (lower quadrant); in both cases the notch is to the right. latter being ventral) ; while the two basally directed quadrants give rise to foot and root (the latter being ventral). The stem and leaf, directed towards the notch, grow under the prothallium and the leaf turns up through the notch. In such a case, the foot is the most temporary organ, functioning only so long as the gametophyte endures, while the primary root does not exist for a long time. The relatively permanent structures of the sporophyte are the stem, giving rise to secondary roots, and the leaves. Apogamy and apospory. —The phenomenon of apogamy is so preva- lent among Filicineae that it deserves special mention. Apogamy is the production of a sporophyte by a gametop

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