PTERIDOPHYTA 



45 



like the higher flowering types, the plant possesses a series of 

 vessels which form a conducting apparatus for the food and 

 manufactured sap. Bryophytes and pteridophytes are some- 

 times called cryptogams ; that is, plants without true flowers and 

 seeds, in distinction to the phanerogams, or higher flowering 

 plants; of these the bryophytes are the cellular cryptogams, 

 and the pteridophytes the vascular. Like the bryophytes, the 

 pteridophytes reproduce by a conspicuous alternation of genera- 

 tions, but differ from the bryophytes in the relative importance 

 of the sexual (reproductive) and the asexual (vegetative) stages. 

 In both, the better known and longer-lived part of the life 

 history is r. presented by a leafy plant which alternates with a less 

 conspicuous phase. The leafy moss plant, however, originates 

 from the spore and produces the male and female elements, 

 while the leafy fern plant originates from the fertilized egg and 

 produces spores. Thus, while the moss plant is the reproduc- 

 tive or gametophyte stage, the fern plant is the vegetative or 

 sporophyte (Fig. ii, D). The life history of the Pteridophyta 

 may be illustrated in general by observing the development of 

 some fern, such as the common Christmas fern. Some of its 

 leaves will be found to bear shorter leaflets near their ends. 

 Upon the under side of such leaflets are rows of small dots, the 

 sori or heaps of spore cases. When one of the tiny spores drops 

 to the ground under conditions where it can germinate it devel- 

 ops into a small, flat, disk-like body, the prothallus. This bears 

 the male and female reproductive organs and from the union 

 of their products, the fertilized egg, grows the leafy fern plant. 

 Thus, in ferns, the sporophyte, which is the leafy plant, and the 

 gametophyte, which is the prothallus, are independent of each 

 other. It has been seen that in mosses the sporophyte is depend- 

 ent on the gametophyte, and it will be seen later that in the 

 higher, flowering plants the gametophyte is completely depend- 

 ent on the sporophyte. 



Derivation of name. — Greek pteris, a fern, + phyton, a 

 plant, in reference to its best known order, the ferns. 



