. Elementary botany. Botany. 346 MORPHOLOGY. 684. The gametophyte may develop directly from the tissue of the sporophyte.—If portions of the sporoi^hyte of ct-rtain of the mosses, as sections of a growing seta, or of the growing capsule, be placed on a moist substratum, under favorable condi- tions some of the external cells Avill grow directly into protonemal threads. In some of the ferns, as in the sensitive fern (onoclea), when the fertile leaves are expanding into the sterile ones, proto- nemal outgrowths occur among the aborted sporangia on the leaves of the sporophyte. Similar rudimeular
. Elementary botany. Botany. 346 MORPHOLOGY. 684. The gametophyte may develop directly from the tissue of the sporophyte.—If portions of the sporoi^hyte of ct-rtain of the mosses, as sections of a growing seta, or of the growing capsule, be placed on a moist substratum, under favorable condi- tions some of the external cells Avill grow directly into protonemal threads. In some of the ferns, as in the sensitive fern (onoclea), when the fertile leaves are expanding into the sterile ones, proto- nemal outgrowths occur among the aborted sporangia on the leaves of the sporophyte. Similar rudimeulary pr(jtonemal growths sometimes occur on tlie lea\"es of the conmion brake (pteris) among the sporangia, and some of the rudimentary spo- rangia become changed into the jirotonema. In some other ferns, as in aspleniuni( A. filix-fcemina, \ar. clarissima ), prothallia are borne among the aborted sjiorangia, which liear anthcridia and archegonia. In these cases the gamctophyte de\'elops from the tissue of the sporophyte without the intervention or necessity of the spores. This is iipospuiy. 685. The sporophyte may develop directly from the tissue of the gametophyte.—In some of the ferns, Pteris crelica for example, the embryo fern spjoroiihyte arises dire<'th' from the tissue of the prothallium, without the intervention of sexual organs, and in some cases no sexual organs are de- veloped on such prothallia. Sexual organs, then, and the fusion of the spermato- zoid and egg nucleus are not here necessary for the development of the spo- rojihyte. This \^ apngamy. Apogamy occurs in some other species of ferns, and . in I'm-is ci-ctio. in other grou])s of plants as well, though it is in general a rare occurrence except in certain spi-cies, where it may be the general 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 re
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