EXPLANATION OF THE PLATES. 
Pirates XVITI-XX.—Curistuas Fern. Polystichum  acrostichoides. 
Plate XVIII.—1-6. Young leaves and plants in early stages of development. 
2. Young plant attached to prothallus. Plate XXIX.—1, 2. Young leaves in 
later stages of development. Plate XX.—1. Mature fertile leaf. 2. Fertile 
pinna of same, X 24. 3. Sterile pinna of same, X 24. 4, 5. Sections of 
sterile pinnz of more highly developed mature leaves, X 24. 
