HORNED I.n'F.RWORTS. 24I 



group of antheridia which lie in a cavity formed around this cell as the 

 thallus continues to grow. They are situated along the middle line of the 

 thallus, and can be seen by making a section in this direction. The anthe- 

 ridia are oval or rounded, have a wall of one laver of cells which contains 

 the sperm cells, and each anthcridium has a slender stalk. The sperms 

 are like those of the true liverworts. 



504. Archegonia. — The archegonia are also b<:)rne along the middle line 

 of the thallus. Each one arises at an earlv stage in the development of 

 the tissue of the thallus from a superficial cell, Vjut the archegonium does 

 not project above the surface. The venter therefore which contains the 

 egg is deep down in the thallus, the waXi of the neck is formed from cells 

 indistinguishable from the adjoining cells of the thaUus and opens at the 

 surface. 



Sporophyte of Anthoceros. 



505. The Sporogonium. — The sporogonium is developed from the fer- 

 tilized egg, fertilization resulting of course from the fusion of one of the 

 sperms with the nucleus of the egg. From the lower part of the embrvo 

 certain cells elongate and push out like rhizrjids into the thallus (gameto- 

 phyte), but never reach the outside so that the sporogonium derives its 

 nutriment from the gametophyte in a parasitic manner hke the true liver- 

 worts. It is surrounded at the base by a sheath, an outgrowth of the 

 gametoph\'te. 



506. Growing point of the sporogonium. — A remarkaVjle thing about 

 the sporogonium of anthoceros, and its relati\'es, is that the gro^^ang point 

 instead of being situated at the free end is located near the base, just above 

 the nourishing foot. Thus the upper part of the sporogonium is older. In 

 the old sporogonia there mav be ripe spores near the free end, "N'oung ones 

 near the middle, and undilTerentiated growing tissue near the base. .\ 

 longitudinal section of a sporogonium just as the spores are ripening will 

 show this. 



507. Structure of the sporogonium. — A longitudinal section of the spo- 

 rogonium shows that the spore-bearing tissue occupies a comparatively 

 small portion of the sporogonium. In the section there is a narrow layer 

 (two cells thick) on either side and joined at the top. In the entire spo- 

 rogonium this fertile tissue is in the shape of an inverted test-tube situated 

 inside of the sporogonium. The wall of the sporogonium is about four 

 cells thick. The sterile tissue inside of the spore -bearing tube is the i:o]u- 

 imlla. The cells of the wall contain chlorophyll, and there are true stomata 

 mth guard cells in the epidermal layer. 



508. Spores and slaters. — In the spore-bearing tissue there are two layers 

 of cells (the archesporium") . Each cell is a potential mother-cell. The 

 ceUs, however, of alternate tiers do not form spores. They elongate some- 



