BRYOPHYTES 295 



consists of a single layer of cells with a rudimentary midrib 

 of elongated thick-walled cells. Both the gametophyte and 

 gametophore obtain their nourishment by means of rhizoids 

 which penetrate the soil. 



The plants are dioecious and the archegonia arid antheridia 

 are borne in the tops of the gametophore shoots. They are 

 slightly different in form but practically the same as the corre- 

 sponding structures in the Hepaticce. Associated with them are 

 clusters of multicellular, hair-like bodies known as paraphyses. 



Fertilization occurs in the same manner as in the Hepaticce, 

 and the young sporophyte develops into foot, seta and capsule. 

 The calyptra, is ruptured near the base and carried upward, rest- 

 ing 011 the capsule as a hood. When the calyptra is removed, we 

 find the operculum or lid-like structure, which can also be re- 

 moved, exposing the peristome. The spores are borne in a 

 cylindrical zone within the capsule. The peristome consists of 

 rows of teeth attached at the rim and pointing inwards. It 

 functions in the distribution of the spores. 



The fully developed moss plant possesses stem-like and leaf- 

 like structures, but a careful study will show that they are very 

 simple as compared with the corresponding organs of the higher 

 plants. The so-called stem is very simple, consisting of elongated 

 parenchyma cells instead of the highly differentiated tissues 

 borne in the stems of the higher plants. The leaf-like organs 

 usually consist of only one layer of undifferentiated cells, except 

 . for a rudimentary midrib consisting of small, elongated cells. 



LABORATORY EXERCISES. 



Exercise 1. Marchantia polymorpha L. 



I. Gametophyte. Examine the thallus. Note its dorsiventral position 

 on the ground, the notch at the tip, its greatest thickness along the axial 

 line, the areas on the dorsal surface and the rhizoids on the ventral surface. 



Examine some of the rhizoids from the ventral surface under the 

 microscope. Note the walls and scattered peg-like projections into 

 the cavity. 



Examine a cross section of the thallus. Note the variation in the cells 

 from the dorsal to the ventral surfaces, especially the epidermal cells, 

 the cells around the stomata and the special chlorophyll-bearing cells 

 within the cavities. 



