The structure & development of the mosses and ferns (Archegoniatae) . foot is very large, andwhile formed originally from theupper hypobasal quadrant, it en-croaches more or less upon allthe others. Very early its cellscease to show any regular orderin their divisions, and divide moreslowly than the other cells of theembryo, so that they become de-cidedly larger. The cells losemuch of their protoplasm as theyincrease in size, and serve simplyas absorbent organs. They are in close contact with the prothallial cells, and crowd upon themuntil the foot penetrates deep into the prothallium, whose c
The structure & development of the mosses and ferns (Archegoniatae) . foot is very large, andwhile formed originally from theupper hypobasal quadrant, it en-croaches more or less upon allthe others. Very early its cellscease to show any regular orderin their divisions, and divide moreslowly than the other cells of theembryo, so that they become de-cidedly larger. The cells losemuch of their protoplasm as theyincrease in size, and serve simplyas absorbent organs. They are in close contact with the prothallial cells, and crowd upon themuntil the foot penetrates deep into the prothallium, whose cellsit partially destroys. It is upon the large development of thefoot, whose outer cells sometimes are extended into root-likeextension like those in Anthoceros, that the young embryo ismaintained so long at the expense of the prothallium. Frequently more than one embryo begins to develop, andsometimes a number of archegonia may be fertilised ; but nocases were met with where more than one embryo came tomaturity, although it is quite possible that this may Fig. 180.—Young sporophyte of O. Clay-toniana, still attached to the prothal-lium, X 6. 352 MOSSES AND FERNS CHAP. The Mature SporopJiyte The growth of the stem in the mature sporophyte is onlyknown in O. regalis} Here there is usually an apical cell of the same type as thatfound in the Ophioglos-saceae or Polypodiacese,but Bower ^ states thatsometimes it is impossibleto refer the tissues to thedivision of a single initialcell, and that there areprobably in these casesseveral initials. Thegrowth of the stem ismuch like that in theother Ferns described,and the structure of theolder parts shows muchthe same arrangement ofthe tissues as that inthe typical vascular bundles,however, are very de-cidedly collateral in struc-ture. A cross-section ofthe stem (Fig. i8i, B)shows a circle of horse-shoe shaped or wedge-shaped bundles, with thexylem directed inwardand bordering directlyupon the pith. Betweenthe
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