114 CLASSIFICATION OF PLANTS 



cluster of colorless cells. The sporophyte, on the other hand 

 is much better developed and constitutes the leafy plant. 



281. Class I. Filicinae. — The Filicinae are the true ferns, 

 a large group of plants of moderate size. A few tropical ''tree 

 ferns" attain the size of a small tree but the more familiar 

 forms have only an underground stem (root-stock) from which 

 the leaves (fronds) rise on long petioles (stipes) to a height of 

 from I to 5 feet. All ferns are holophytic. Many species, 

 especially tropical ones, are epiphytic. 



282. The gametophyte of the fern is a small green thalloid 

 structure (prothallium) which lies flat on the ground. (Or 

 colorless, saprophytic and underground, Order i.) Embedded 

 in its tissues are the antheridia and archegonia. The anthero- 

 zoids are spiral bodies with a tuft of ciHa at one end. The 

 fertilized egg cell divides into four segments from which are 

 developed root, stem, leaf and foot respectively. The foot is 

 an organ by which the developing plant retains connection 

 with the prothallus for some time. The prothallus finally 

 disintegrates and the plantlet becomes independent. The 

 plant with the root, stem and leaves is the sporophyte. The 

 spores are developed in sporangia on the under surface of the 

 leaves. Sometimes the spore-bearing portion of a leaf is espe- 

 cially modified, or again the spores are only borne on certain 

 leaves which then are completely modified (sporophylls). 



283. Order 1. — The Ophioglossacece or adder-tongue ferns, are a small 

 group of slow growing and rather inconspicuous plants. The gametophyte 

 is a small, saprophytic, underground thallus. The leaf is partly differ- 

 entiated into sporophyll. 



284. Order 2. — The MaraitiacecB are tropical ferns of large size. The 

 prothallus is a green thallus resembling a liverwort. The sporangia are 

 grouped in sori on the under surface of the foliage leaves. 



285. Order 3. — The Filices are the order to which most of our common 

 ferns belong. Most of the tropical tree ferns also belong to this order. 

 The order comprises many genera and species. Many are epiphytic. 

 The gametophyte is usually a small, green, liverwort-like prothallus which 



