REPORT ON THE PHILOSOPHY OP BOTANY. 31 



It would, however, appear from the researches of Mirbel *, 

 tliat the presence of a twisted fibre within a cell is not always 

 the cause of the spiral or fibrous character so common in tissue. 

 He finds, as has been already stated, that the cells that line 

 the anther of a gourd are at first membranous and closed, and 

 that they continue in this state till just before the bursting of the 

 anther, when they suddenly divide in such a way as to assume 

 the appearance of delicate threads, curved in almost elliptical 

 rings, which adhere to the shell of the anther by one end ; these 

 rings are placed parallel with each other in each cell, to which 

 they give an appearance like that of a little gallery with two 

 rows of pilasters, the connecting arches of which remain after 

 the destruction of the roof and walls. He also watched the 

 development of the curious bodies called elaters in the Mar- 

 chantia, which he describes to the following effect. At first 

 they are long slender tubes, pointed at each end ; at a subse- 

 quent stage their walls thicken, and become less transparent, 

 and are marked all round through their entire length with two 

 parallel, very close, spiral streaks ; later still the tubes enlarge, 

 and their streaks become slits, w^iich divide the walls all round, 

 from one end to the other, into two filaments ; and, finally, the 

 circumvolutions of the filaments separate, assume the appear- 

 ance of a corkscrew, acquire a rust colour, and the elater is 

 complete. These elaters he considers organically identical with 

 the spiral vessel, and hence he concludes that every description 

 of vessel is a cell, differing from ordinary cells in being larger. 



Upon the general accuracy' of these observations I am dis- 

 posed to place great confidence ; and I would even add, that the 

 theory of pierced or open cellular tissue being produced by 

 the spontaneous rending of its membrane, is apparently con- 

 nected with an observation of my ownf, that in some plants 

 simple vegetable membrane will tear more readily in one direc- 

 tion than another. It is nevertheless to be observed, that the 

 theory of fibre being one of the organic elements of tissue does 

 not seem to have occurred to the experienced physiologist to 

 whose observations I am referring, and that some of the ap- 

 pearances he mentions at a stage preceding transformation are 

 very like those of the development of an internal fibre. 



The opinion of the organic identity of all the forms of tissue 

 has also been maintained by Mr. Slack, in the paper already 

 referred to, and by Dr. Mohl, in his memoir on the comparative 

 anatomy of the stem of CyeadecBt Conifers, and Tree Ferns. 



* Archives de Botanique, vol. i. 

 t Introduction to Botany, p. 2. 



