OF ARTS AND SCIENCES. 217 



Fig. 19. Diagram of a portion oi a transverse section still lower down. L, L = 



limiting layers ; C, C := conical layers. X 385. 

 Fig. 19 a. Diagram of a small portion of a similar section showing two young 



sclerenchyraa fibres. X o85. 

 Fig. 20. Diagram of a portion of a longitudinal section in the same portion of 



the blade as that represented m Fig. 19, with tlie same lettering. The 



shaded baud m the middle represents a young sclerenchvma fibre. X 3b5. 



Plate II. 



Fig. 21. Diagram of a portion of the centre of a transverse section through a 

 rhizogen which has produced one set of hapteres. a, sclerenchyma cells; 

 b, hyphal cells. X 500. 



Fig. 22. Diagram of a section through the centre of a young cryptostoma in 

 the transition place of a frond about 20 cm. long. X 500. 



Fig. 23. Diagram representing portions of two elongated cells of the inner 

 cortex of a young specimen, showing the thickenings around the pits. 

 X 500. 



Fig. 24. Diagram of a small portion of the margin of a transverse section of 

 the stipe of a specimen collected at Nahant in September, 1889 L = the 

 limiting layer ; a = a couple of cells which have recently divided off from 

 the peripheral cell. X 500. 



Fig. 25, a, b, c. Diagrams of tips of sclerenchyma fibres seen in median longi- 

 tudinal optical section From a specimen collected at Nahant m December, 

 1889. X 385. 



