THE LIFE HISTORY OF A MOSS 



295 



the protonema change their methods of cell division and develop 

 small buds (Fig. 262, pi) which grow into the leafy moss plants 

 (F"ig. 263). One moss spore may give rise to a great quantity of 

 protonema, which by means of the numerous buds will form a 

 large group or even a turf of moss plants. Therefore the protonema 

 is a very effective means of establishing the large carpets of moss 

 vegetation. The leafy moss plant develops the sexual organs in 

 clusters at the top of the stem 

 and has further peculiarities of 

 structure which will be described 

 later. The protonema together 

 with the leafy moss plant consti- 

 tute the sexual or gametophyte 

 phase of the life history. 



The fertilization of an egg in 

 an arehegonium starts at once the 

 development of the sporophyte, 

 often called the moss fruit. The 

 fertilized egg gives rise to a many- 

 celled structure (Fig. 264, A), 

 which establishes a growing point 

 above and a foot attachment to 

 the gametophyte below. This 

 young sporophyte is contained at FIG 20g A young plant of a com . 

 first entirely within the parent mon moss (Webera) 



arehegonium, which enlarges with Showing its attachment to the proto- 



its development (Fig. 264, B, a). nemal filaments which bear repro- 

 T^ , n v, ,, ductive buds 6 



But finally the growth of the 



sporophyte is so rapid that the arehegonium is torn away at its 

 base and borne upwards on the elongating stalk of the sporo- 

 phyte. The remnant of the arehegonium then covers the tip of 

 the stalk like a cap (Fig. 265, B, cal) and is called the calyptra 

 (meaning a veil), which must serve a useful purpose, protecting 

 the delicate growing tip of the sporophyte. Finally, the tip of 

 the sporophyte enlarges and becomes the complex spore case 



