Nature and development of plants . ale gamete which is surrounded by nour-ishing cells as in the cycads. You notice that there is no cham-ber formed above the archegonia, and it would be a natural infer-ence that the male gametophyte must be of a somewhat differentcharacter from that of the cycads in order to meet this new de-parture. The microspores which have already begun to germi-nate when discharged from their sporangia are carried by thewind to the megasporophylls which are slightly spread apart atthis time, permitting the microspores to rattle down to the mega-sporangia. The microspores
Nature and development of plants . ale gamete which is surrounded by nour-ishing cells as in the cycads. You notice that there is no cham-ber formed above the archegonia, and it would be a natural infer-ence that the male gametophyte must be of a somewhat differentcharacter from that of the cycads in order to meet this new de-parture. The microspores which have already begun to germi-nate when discharged from their sporangia are carried by thewind to the megasporophylls which are slightly spread apart atthis time, permitting the microspores to rattle down to the mega-sporangia. The microspores fall into the micropyle either byreason of the position and construction of the megasporangia,which may be so placed that the spores naturally roll down into 33& GAMETOPHYTE OF PINE the micropyle, or the microspores may be drawn through the mi-cropyle by mucilaginous excretions as in the cycads. The earlystages in the germination of the microspore are essentially as inCycas, though more reduced. The microspore on reaching the. roc Fig. 253. Megasporangia of pine: A, scale-like outgrowth of sporophyllhearing two sporangia. B, section of A, taken through one of the spo-rangia, showing the sporophyll, s, and large scale-like outgrowth whichbears the sporangia, sp. The sporangium is surrounded by an integument,i, and contains a single megaspore, m, as in the Cycads. mc, microsporesthat have been drawn through the micropyle to the sporangium, into whichtheir tube cells are growing. C, section of megasporangium enlarged anddiagrammatic, showing the female gametophyte at the time of fertilization—g, female gametophyte, showing two archegonia with large female ga-metes, fg. At the left the tube of the microspore, mc, has entered the neckof the archegonium and the two male gametes have been discharged intothe large sac of the female gamete. On the right the tube cell with malegametes is seen approaching the neck of the archegonium. i, integument;sp, remains of sporangium not disorgan
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