EXPLANATION OF THE PLATES. 



PLATES XVTII-XX. CHRISTMAS FERN. Polystichum acrostichoides. 

 Plate XVIII. 1-6. Young leaves and plants in early stages of development. 

 2. Young plant attached to prothallus. Plate XXIX. i, 2. Young leaves in 

 later stages of development. Plate XX. i. Mature fertile leaf. 2. Fertile 

 pinna of same, X 2^. 3. Sterile pinna of same, X 2^. 4, 5. Sections of 

 sterile pinnae of more highly developed mature leaves, X 2^. 



