. A handbook of cryptogamic botany. Cryptogams. GINELLA CE^ 39 Order i.—Selaginelle^. In the genus Selaginella, the sole representative of the order, the prothallium appears to be already completely formed by the time the megaspore is mature, but occupies only the apical portion of the cavity of the spore; the basal portion is still filled by an undifferentiated mucilagi- nous protoplasm, which subsequently develops into a cellular tissue, the second- ary prothallium, or, -as it is termed by some writers, the endosperm. In some species, at least, this struc- ture is separated by a dia- p
. A handbook of cryptogamic botany. Cryptogams. GINELLA CE^ 39 Order i.—Selaginelle^. In the genus Selaginella, the sole representative of the order, the prothallium appears to be already completely formed by the time the megaspore is mature, but occupies only the apical portion of the cavity of the spore; the basal portion is still filled by an undifferentiated mucilagi- nous protoplasm, which subsequently develops into a cellular tissue, the second- ary prothallium, or, -as it is termed by some writers, the endosperm. In some species, at least, this struc- ture is separated by a dia- phragm from the true pro- thallium. The prothallium always produces a number of archegones, sometimes as many as thirty, which arise in centrifugal succes- sion on the exposed portion of the prothallium, the one formed first being at the apex. The archegone ori- ginates by division of a superficial cell in a direction parallel to the surface ; the outer of these two then divides into four cells, and each of these again breaks up by tangential division into two. These form the neck of the archegone, which therefore consists of four rows, each composed of two cells. The lower of the two original cells becomes the venler of the archegone, and puts out a slender prolongation between the neck-cells, which is separated as the neck-canal-cell. Another yery sma,ll pprtion is subsequently separated. Fig. ao.—A—F^ stages in the division of the microspore of Selaginelta, eaulescens Spr, v, sterile cell; G, antherozoid ( X 1400); H^ vertical section of megaspore of 6". Mar- fgnsuSpr, ;^, prothallium with three archegones; end, en. dosperm; e, exospore (x 165), (After Pfeffer.). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bennett, Alfred W. (Alfred William), 1833-1902; Murray, George Robert Milne, 1858-. Lo
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