43 



little warts*. An observer must be very unskilful, who having 

 such a Sphagnum before him should overlook the pores. It 

 follows from the above, that it cannot be laid down as a gene- 

 ral rule, that the septa of Sphagnum are perforated by great 

 pores, for there are some which remain to the very end of their 

 life destitute of them. 



At the end of the above dissertation M. Mohl has pub- 

 lished various observations against the metamorphosis of spi- 

 ral fibre into annular fibre, a phaenomenon which he desig- 

 nates as one founded upon no fact and purely hypothetical, 

 while I have again defended this alleged hypothesis. The 

 annular spiral ducts originate only from those simple spiral 

 tubes whose sides consist of a single or of few spiral fibres ; 

 thus I observed in a common bean an annular duct, which 

 belonged to a spiral tube of two spiral fibres. In order to 

 show the improbability of this division of the spiral fibre 

 into definite portions, M. Mohl asks by w r hat force could such 

 a division of the spiral fibre be effected. However, this ques- 

 tion may easily be answered ; for can we not actually observe 

 in a thousand other cases a similar division of simple thread- 

 like formations into pieces of a like size, especially the con- 

 striction of such into articulations and sporangia? But even 

 the separation of the spiral fibre is actually to be seen in some 

 places, as for instance, in Cactus cylindricus, where the spiral 

 fibres, which there generally occur separated in rings, are very 

 large ; it is only necessary to assist here a little with the knife, 

 and the spiral fibre breaks or falls into the proper position, 

 which always corresponds to the other free extremity, so as to 

 form with this a perfectly closed ring. The reason that the 

 division of the spiral fibre does not take place under our eyes, 

 as is the case with many similar phaenomena, is evidently 

 this ; because this process happens at the very earliest forma- 

 tion of the spiral tubes, and hitherto no one has observed 

 the formation of spiral fibre. If we examine long portions of the 

 beautiful simple spiral tubes in the stem of Tradescantia and of 

 the common bean ( Vicia Faba) we observe that in the course 

 of the complete spiral tube some small places occur where the 

 spiral fibre has become converted into rings ; nay, below these 

 rings, there exist again frequently some, which still consist of 

 Pflanzen-Physiologie, ii. 52. 



