212 - Multicellular Planfs 



tophyte generation retains a capacity to re- 

 produce by sporulation. 



LIFE CYCLE OF THE MOSSES 



Mosses, the most familiar of the Bryo- 

 phyta, are small green leafy plants, which 

 grow in densely crowded masses, on damp 

 and shaded soils (Fig. 12-11). Mosses are not 

 well adapted to terrestrial conditions, and 

 most species cannot survive in dry localities. 

 Most mosses are relatively short plants, with 

 an average height of only about half an inch. 



The small green leafy-stemmed moss plant 

 is a gametophyte — that is, a haploid gamete- 

 producing individual. The crowded leaves 

 all originate from a single central stem, 

 which cannot be seen unless the leaves are 

 plucked away. Numerous rhizoids extend 

 down into the soil horn the lower end of the 

 stem. The rhizoids absorb water and inor- 

 ganic salts for the upper green parts of the 



plant, which, in return, provide the rhizoids 

 with glucose. Accordingly, the gametophyte 

 of the moss is a small but independent plant, 

 which displays a typically holophytic nu- 

 trition. 



The antheridia, or archegonia, depending 

 upon the sex of the gametophyte, develop 

 at the top of the stem, hidden by the en- 

 circling upper leaves — Figure 12-12. In the 

 mature female plants, a single large egg cell 

 is found in the venter of each archegonium 

 (Fig. 12-12). The sperm are liberated in 

 swarms (Fig. 12-12) from the antheridia 

 (Fig. 12-12) of the male plants during peri- 

 ods of rain or heavy dew. Each sperm (Fig. 

 12-12) is a delicate elongate cell possessing 

 two flagella, which enable the sperm to swim 

 through water to a neighboring female plant. 

 Some sort of chemical attraction appears to 

 emanate from the neck of the archegonium, 

 and thousands of sperm may simultaneously 

 attempt to swim down this narrow passage. 



Fig. 12-11. A clump of moss plants (Polytrichum). The leafy (lower) part of each plant 

 is a gametophyte, from the top of which grows the slender-stalked sporophyte. The 

 conspicuous white spindle-shaped bodies are the sporangia of the sporophytes. (Photo- 

 graph by t. W. Brownell, retouched.) 



