EXPLANATION OF THE PLATES. 

 Plates XVIII-XX. — Cheistmas 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^. 



