216 PROCEEDINGS OF THE AMERICAN ACADEMY 



EXPLANATION OF THE FIGURES. 



Platk I. 



Fig. 1. Diagram of a very young plant ratlicr narrower than the typical form. 

 Tlie midrib-like portion is shaded. X 10. 



Fig. 2. Diagram of a very young plant of the typical form. The midrib-like 

 portion is shaded as in Fig. 1. X 10. 



Fig. 3. Sketch of a young plant from Nahant, showing no trace of a rhizogen. 

 A = the primitive disk ; C = the stipe ; D — the more complex blade ; E = 

 the primitive blade. X 1.75. 



Fig. 4. Sketch of a young plant showing the rhizogen at B. Other letters as 

 in Fig. 3 X 1. 



Fig. 5. Sketch of a young plant in wliich the hapteres are just appearing. 

 X 1. 



Fig. 6. Sketch of a plant somewhat more advanced. Xl 



Fig. 7 Sketch of the base of a young plant in which the hapteres (F) are well 

 developed, but in which the primitive disk (A) still persists. X 1- 



Fig. 8. Diagram showing the point of attachment of the primitive disk ( 1) and 

 of each of the first set of hapteres (2). X 1. 



Fig. 9. Sketch of the base of a young plant showing the primitive disk (A) 

 still remaining, the first set of hapteres attached, and the second set of hap- 

 teres just appearing. X 1. 



Fig. 10. Sketch of the base of a small adult plant collected at Nahant in 

 February, 1890, showing the permanent holdfast, the flattened stipe, and the 

 " oar-shaped " base of the blade. X 1- 



Fig. 11. Tracing of the outline of the base of a young plant having the appear- 

 ance of " renewing the blade." At A is the constriction between the young 

 and the adult portions. X 1 



Fig. 12. Diagram of a portion of a transverse section of the blade of a speci- 

 men 1.2 cm. long, showing at A and A the beginnings of the more complex 

 portion. X 500. 



Fig. 13. About 80 n below the section represented in Fig. 12. X 500. 



Fig. 14. Diagram of a portion of a transverse section still lower down on the 

 same plant, showing the three-layered blade in the centre and the one-layered 

 blade on the sides. In the very centre is sliown the transverse section of a 

 young sclcrenchynia fibre, and at one side are the bunches of hairs belonging 

 to young cryptostomata. X 500. 



Fig. 15. Diagram of a little more than half of a transverse section below that 

 represented in Fig. 14, showing the proportion existing between the three- 

 layered blade of the centre and the one-layered blade at the sides. X 385. 



Fig. 16. Diagram of a portion of a transverse section below that represented 

 in Fig. 15. X 000. 



Fig. 17. Diagram of a portion of a transverse section showing at B the origin 

 of a second more complex portion of tlie blade. At A is the transverse sec- 

 tion of a sclerenchyma fibre. X 385. 



Fig. 18. About 15 IX below Fig. 17. a, a, represent transverse sections of 

 young sclerenchyma fibres. X 385. 



