2 American Midland Naturalist Monograph No. 6 



antheridia absorb water and the thin wall, consisting of but a single layer of 

 sterile cells, is ruptured, thus liberating the mass of fertile cells, each of which 

 immediately develops into a sperm. Each sperm consists of a more or less 

 oval or club-shaped and curved body, always free-swimming by means of two 

 long slender cilia attached at one end of the body. 



The egg is borne in a special organ termed the archegonium. The arche- 

 gonium is usually more or less stalked and is differentiated into a swollen 

 basal portion termed the venter, which contains the one fertile egg cell, and 

 the more slender tapering neck, terminating the archegonium above and con- 

 taining an axial row of sterile cells termed the canal cells, the basal one of 

 which rests directly upon the egg cell. When the archegonium becomes ripe 

 the canal cells break down into a slimy mass of protoplasm, some of which may 

 escape at the tip of the neck. Sperms are attracted in some m.anner by the 

 slimy protoplasm thus escaping if there is a sufficient film of moisture present 

 so that they may swim about in the perichaetium or on the surface of the 

 plant. Having reached the apex of the archegonium the sperms may enter the 

 canal left open by the disintegration of the canal cells and eventually one of 

 the sperms may reach the eggs and, uniting with it, brings about fertilization. 



After fertilization the egg immediately begins development as the sporo- 

 phyte but remains enclosed in the venter of the archegonium, which to a con- 

 siderable extent expands with the development of the young sporophyte but is 

 finally ruptured and usually carried upward on the tip of the sporophyte, 

 where it is then known as the calyptra or hood. The ultimate end of the 

 sporophyte is the production of spores which arise entirely by division of cells 

 and are thus known as asexual cells. The sporophyte is usually almost devoid 

 of chlorophyll and it develops at its base an absorbing organ termed the foot 

 through which its food is obtained from the gametophyte. The sporophyte 

 usually develops more or less of a stalk which is termed the seta and which 

 bears at the apex a globose to more or less elongated capsule in which the 

 asexual spores form. The method of opening (dehiscence) of the capsule and 

 the structures often associated with the dispersal of the spores are varied and 

 are so characteristic for the various systematic groups and species that the cap- 

 sule becomes highly important for the correct systematic placing of the plants. 



Of the mosses there are to be distinguished three well-marked orders 

 known as the Sphagnales, the Andreaeales, and the Bryales. The order Sphag- 

 nales comprises the one genus Sphagnum. These mosses are known as peat 

 mosses or bog mosses, their most characteristic habitat being bogs and the 

 margins of ponds and small lakes. The general color is grayish green, the 

 stems are usually erect in dense tufts or mats and bear at intervals fascicles of 

 short and slender branchlets. The capsules are usually more or less chestnut- 

 colored and globose, while the leaves possess a peculiar and characteristic 

 structure consisting of a meshwork of slender green cells enclosing inflated 

 hyaline cells whose walls are more or less porose. 



The Andreaeales contain the one genus Andreaea, all being small tufted 

 mosses growing on siliceous rocks in mountainous regions. The capsule splits 



