Mosses and Their Allies — Bryophytes 187 



oogamy (o-og'ami) (Gr. 0072^ egg; gamos^ marriage). In oogamy the 

 two gametes are unlike and the eg^ is stationary. The fertilized ^^^, 

 known as a zygote, is retained in the venter where it forms an embryo 

 by numerous cell divisions. The embryo is parasitic on the female 

 gametophyte plant, being given water, food, and protection. The embryo 

 then grows to form a new plant known as the sporophyte (spor'ofite) 

 (Gr. sporos, spore; phyta, plants). A sporophyte consists of a foot, 

 which is attached to the female plant, and a stalklike seta, at whose tip 

 is a spore case or sporangium (spor -an' ji um) (Gr. sporos, spore; ang- 

 geion, vessel). The sporangium, or capsule is covered with a hairy cap 

 or calyptra (ka -lip' tra) (Gr. kalyptra, covering) ; hence the common 

 name of hairy cap. When the calyptra is removed, a lidlike operculum 

 (o -per' ku lum) (L. operculum, lid) is observed to cover the capsule. 

 Beneath the operculum is a ring of hygroscopic teeth known as the peri- 

 stome (per'istom) (Gr. peri, around; stoma, opening). The teeth are 

 affected by moisture, and their movements expel the spores from the 

 capsule. When immature, the capsule contains spore mother cells, each 

 of which undergoes reduction division (meiosis) and produces four 

 spores. The four spores of each tetrad are of two kinds. One kind con- 

 tains a small, Y chromosome (sex chromosome) and produces a male' 

 plant; the other kind contains a large, X chromosome and produces a 

 female plant. This method of sgx determination is similar to that in 

 man in which there are also X and Y chromosomes. 



Each spore germinates to form a threadlike, branched protonema 

 (pro to -ne' ma) (Gr. protos, first; nema, thread). The cells of the 

 protenema bear chloroplasts with which to photosynthesize food. Rhi- 

 zoids anchor the young plant and absorb materials from the soil. Buds 

 appear on the protonema, and these, by cell divisions, produce a new 

 male or female moss plant. There is an alternation of generations be- 

 tween the gametophyte plant and the sporophyte plant. Under certain 

 conditions some mosses may reproduce asexually by a fragmentation of 

 the plant or by the formation of special bodies known as gemmae (jem' i) 

 (L. gemma, bud) . 



2. Sphagnum (sfag' num) (Gr. sphagnos, moss) is the name of a genus 

 to which belong the peat or bog mosses which are common inhabitants 

 of bogs, ponds, and other wet places. Their life cycles are similar to that 

 of Polytrichum. The upright, branched axis may be one foot long and 

 bears leaflike appendages ("leaves") (Fig. 46). The latter contain two 

 types of cells — one for water storage and the other containing chloroplasts 



