Meyen's Report for 1 839 on Physiological Botany. 251 



M. Schleiden convinced himself of the homogeneousness of 

 this membrane. I formerly made known, that in old coniferous 

 wood there is often an actual splitting of the entire walls of 

 the cellular membrane, always in the direction of the juncture 

 of the spiral bands of which the walls are composed, and that 

 these clefts, \^hich are often very large, al^^ays pass through 

 the pores.] 



The reticular figures on the bast-cells of the Apocytiea, M. 

 Schleiden derives from the superposition of two very fine lay- 

 ers which consist of oppositely wound spirals ; and finally, he 

 makes some remarks on the direction of the windings of spi- 

 rals. M. Schleiden has laid down the following rule : — Of all 

 spiral formations which are developed simultaneously, those 

 which lie together in the direction of the radius are homodro- 

 mous, those which lie together in the direction of the parallels 

 to the periphery are heterodromous. As exceptions are men- 

 tioned the annular and spirally fibrous cells of the Cacti ; but 

 as confirmatory of the first statement, the general crossing of 

 the pore-clefts of neighbouring cells, which was first observed 

 by me, is brought forward. 



M. Mohl* has endeavoured to disprove some of the views 

 of M. Schleiden with which he does not agree, particularly 

 that one, as M. Mohl says, which has extended to the present 

 time, but is perfectly false, viz. that the annular vessels are 

 produced from spiral vessels. He says, that even since the ap- 

 pearance of Schleiden's new theory, he still adheres to his 

 former statements with regard to their origin, 



M. Mohl first gives some descriptions of the structure of 

 the spiral and annular fibres in their perfect state, in order to 

 make clearer some points which M. Schleiden in his observa- 

 tions on the formation of the annular tubes had stated incor- 

 rectly ; he describes particularly the lines and grooves which 

 are often seen on the broad fibres of the Commelinea. Some- 

 times these lines and grooves penetrate the whole thickness 

 of the fibre, so that it is divided in some places into two or 

 three fibres, and these either proceed in their course parallel 

 to each other, or then join again after a longer or shorter 

 course, or one of these fibres passes in a more perpendicular 

 direction than the others, and joins the next whorl of the fibre. 



The direction of the winding of the spiral fibre is next 

 spoken of: he had formerly shown that the spiral vessels are 

 generally wound to the right, and he states that he cannot 

 agree with M. Schleiden and other phytotomists who main- 



* Flora von 1839, p. G73 — GS.^, &c. Traiisliitcd at p. 10 of" our present 

 volume : sec also Dr. Schleiden in reply at p. 2o. 



