Plant growth substances like Auxins, Gibberellins an Ethylene induced apogamy in several species of ferns. Cytology of Apogamy: The chromosome number of the apogamously produced sporophyte will be similar to that 06 the gametophyte. Usually, the gametophytes are baploid and the apogamously produced sporophytes also will be haploid In some instances, the gametophytes are diploid (they ar produced aposporously from the sporophyte). When sue diploid gametophytes apogamously produce sporophytes, th sporophytes also will be diploid.
In obligate apogamous species, there is an alternation 0 2n sporophyte with 2n gametophyte . The sporophyt is diploid (2w). Before meiosis, the chromosome number doubled (4w) by a process called syndiploidy. Diploid (In spores (meiospores) are produced by meiosis, and the produce the diploid gametophytes. The diploid gametophyte apogamously produced diploid sporophytes. If the chromosome number is not doubled (An) in the sporophyte, th chromosomes will not pair during meiosis and this wil result in abortive spores. The viable spores are those whic have the same number (2M) as the sporophyte (2n).
It is a departure from the classical sexual cyile, wh;re there is an alternation of diploid sporophyte with haploid gameto¬phyte. In a sexual species, the sporophyte has 64 viable spores In a sporangium, but in an apogamously produced sporophyte, the number of viable spores in each sporangium is 32. Some sporangia have 64 abortive spores.
Syndiploidy followed by meiosis are, therefore, the two characteristic processes of apogamous cycle. But, there are some exceptions also. Potypodium dispersum is an obligate apogamous fern. In its life cycle, both synploidyand meiosis are absent. The entire life cycle is accomplished by mitotic divisions . The diploid sporophyte by mitosis produces diploid spores (Diplospores), which on germination produces diploid gametophytes.
These diploid gametophytes apogamously produced diploid sporophytes. The life cycle of this fern is unique itt the sense that the entire cycle is asexual and the syngamy^ meiosis and the genetic recombina¬tions do not take place. Such a diploid spore formation has been reported in Ophioglossum. Isoetes, Asplenium, Gymnocar-pium, Polypodium, Polystichum and Pteris. In Nephrodium pseudo-mass rom.cristata the gametophte apogamously produced a sporophyte, which in turn aposporously produced a gametophyte . The same is observed in Trichomanes alatum and Athyrium fllx-foemine
