41 



exist however on this subject, and are as diametrically op- 

 posed to one another as those on the metamorphosis of the spi- 

 ral tubes. According to M. Schultz, constrictions and the for- 

 mation of articulations of the proper vessels originate with the 

 advancing age of the plant ; in the young state these vessels 

 were still unarticulated. According to my observations, the 

 proper vessels are neither in their youth nor old age provided 

 with cross partitions, but exhibit in the latter state some con- 

 strictions which are independent of external circumstances. 

 According to M. Mohl, the continuous vessels of the latex ori- 

 ginate from cells, whose cross partitions disappear, to which, in 

 consequence of numerous researches on this subject, I am 

 decidedly opposed. 



The distinction between dotted and reticulated spiral tubes 

 consists, according to M. Mohl, in this ; that in the latter the 

 organic matter used for the further development of the vessels 

 does not deposit itself in the form of a membrane between the 

 coils of the spiral fibre, but goes to increase the spiral fibre 

 itself, both with respect to its thickness as well as to its 

 breadth. In the dotted (porous) spiral ducts of dicotyledons, 

 on the contrary, this substance is deposited in the form of a 

 membrane between the coils of the spiral fibre on the original 

 membrane of the vessel. 



Neither can I concur in these statements : the thickening 

 of the walls of both those stages of metamorphosis of the spiral 

 tubes takes place in quite a similar manner ; the principal 

 reason for the change into reticulated and into dotted spiral 

 tubes is to be found only in the arrangement of the individual 

 coils of the spiral fibre. If the coils are widely apart they 

 may fall merely into annular tubes or be metamorphosed into 

 reticulated spiral tubes ; on the contrary, if the coils are close 

 together, only striped and dotted spiral tubes and not reticu- 

 lated can originate. This is very easily confirmed in stems of 

 Cacti, in the inflorescence of Musa, &c. 



On the occurrence of spiral fibre and of pores in the cellular 

 septa of the leaves of Sphagnum much has already been written ; 

 but, as it appears, this subject will be first cleared up in the 

 present year (1838), and that by my having now discovered 

 the cause which gave rise to the different views of various ob- 

 servers on this subject. Even many years ago there existed a 



