Il6 THE BRACKEN-FERN. 



parts of the oospore is a marked advance over Bryophytic 

 conditions. 



The sporophyte, which in Bryophytes is always para- 

 sitic, is here a prominent structure bearing extensive 

 leaf surfaces, thereby exposing much chlorophyll to 

 the light. This increase in chlorophyll work is neces- 

 sarily accompanied by an increase in mechanical and 

 conducting tisues. The conducting system is far superior 

 to anything seen in Bryophytes, as is also the mechanical 

 system. The leaf-stalk supports the chlorophyll tissue, 

 the real stem being underground, where it serves as the 

 axis for the secondary root system, and also serves as a 

 storage region for surplus food. 



For the development of the organs of the plant, 

 gametophyte, root, stem, etc., growth is localized; and 

 in each such locality there is present a specialized cell, 

 the apical cell, from whose faces new cells are cut off 

 by partition-walls. After each division it enlarges, and 

 repeats the process on another face. Adjacent cells 

 also divide and grow, and this may occur anywhere. 

 But the apical cell is very active in division, and thus 

 marks a region of growth. 



Sporangia arise from a single surface cell, which is 

 indicated by saying that this plant is leptosporangiate. 

 The sporangia are stalked and have a special structure, 

 the annulus, for the distribution of spores. 



This plant exemplifies well the order Filicales, the 

 true ferns, one of the chief orders of Pteridophytes. 



