496 Mr. Valentine on the Structure and Development 



Tab. XXXV. 



Fig. 20. The termination of a growing brancii, with two young leaves and 

 four roots in various stages of advancement, a. Is a root before it has 

 burst through its sheath, b. The sheath which envelopes the tip 

 of the root. c. A young bud, from which may be produced either a 

 branch and leaves and roots, or an involucrum : it is impossible to 

 distinguish one bud from the other in the youngest state. All the 

 buds and growing extremities of the branches are clothed with hairs, 

 which fall off as the part becomes developed. 



Fig. 21. An involucrum about half matured ; it is densely covered with hairs, 

 which gradually decay and fall off, so that there are only a few de- 

 cayed remnants left on the mature involucrum. 



Fig. 22. A hair from an involucrum. a. The point of attachment. 



Fig. 23. A hair from a bud. a. The point of attachment. 



Fig. 24. Section of a leaf, showing the central bundle of vessels surrounded by 



(. enlarged cells; the partitions, and a diaphragm. 



Fig. 25, Section of a root, showing two of the gyrate bodies, which are fre- 

 quently found in the cavities of the root. 



Fig. 26. A portion of the cuticle of the leaf with stomata. 



Fig. 27. Longitudinal section of a leaf, giving a view of a partition, and the 

 central bundle of spiral vessels. 



Fig. 28. A portion of the tissue which forms the partition in the root. 



Fig. 29. Section of a young involucrum. In this stage the three outer coats 

 are of a very faint brown colour, and the inner quite colourless. The 

 two middle coats are drawn scarcely thick enough. The thecae 

 contain sporules in the first and second stage of development ; they 

 are too opake, however, to show their contents with any distinct- 

 ness. 



Fig. 30. Section of a mature involucrum from about the middle, so that it 

 contains both kinds of thecee ; those containing fertile sporules, and 

 those which are occupied by the abortive ones. 



Fig. 31. A union of sporules in their first stage ; the mother-cell is not visible 

 in this stage : — magnified 200 times. 



