We have selected the seedless vascular plants for this exercise because

- they most clearly illustrate the alternation of gametophyte and sporophyte generations.

- both generations are independent and free-living; neither generation is nutritionally or structurally   dependent on the other.

Remember from last week when the life cycle was discussed for the multicellular brown algae or kelp that

- sporophyte and gametophyte generations alternate with each other.

- a sporophyte, by definition, is a diploid plant body which produces spores by meiosis. Sporophytes  may reproduce asexually.

- a gametophyte is a haploid plant body which produces gametes by mitosis. Gametophytes reproduce  sexually.

- meiosis, in plants, does not directly produce gametes unlike in animals.

In the seedless vascular plants on display this week,

- gametophytes produce sporophytes by sex and sporophytes reproduce gametophytes asexually.

- the sporophytes are large, long-lived and vascular, with many structural modifications for life on  land. The gametophytes are microscopic, non- photosynthetic (except in the horsetails and ferns),  non-vascular and short-lived.

- periodic moisture is necessary for fertilization of the egg by flagellated sperm and for the survival of  the non-vascular gametophyte.

Division Lycophyta: live Selaginella, live Lycopodium - both with vegetative growth only; jar with preserved Lycopodium strobili.

- strobili contain sporophylls (specialized leaves) which give rise to spores meiotically.

- in Selaginella, two kinds of spores are produced (heterosporous) which give rise to separate male and  female gametophytes. In Lycopodium only one kind of spore is produced (homosporous) which gives  rise to gametophytes with both male and female organs. Self fertilization is common.

Division Sphenophyta: living vegetative Equisitum sporophyte and preserved strobili.

- interesting as garden pests (horsetails) which are dificult to get rid of because of underground  rhizomes.

- store silicon in stem (evolved probably as a protection from grazing animals).

- strobili produce one kind of spore (homosporous) which gives rise to bisexual gametophytes. Self  fertilization is common.

Division Pterophyta: 2 ferns, both with sori.

Most ferns produce one kind of spore (homosporous) but have evolved a way to prevent self fertilization.

Slides: A. male and female gametophyte

Fern gametophytes are bisexual (monoecious), but their antheridia mature earlier than their archegonia. This prevents self-fertilization. Because 'female' gametophyte is older, it is larger than 'male' gametophyte. Sperm and eggs are produced by mitosis.

Fern sporangia are aggregated in areas called sori under leaf of fern. Sporangia produce spores (N) by meiosis.