44 Dr. M. J. Schleiden on Spiral Formations. 



layers of the oldest heart wood constantly exhibited more or 

 less distinctly these delicate stripes, and the pores then again 

 appear merely as narrow clefts between two separating spiral 

 coils. 



In consequence of this view of mine of the constant gene- 

 rality of the spiral arrangement of the secondary depositions, 

 I am also inclined, for the sake of consistency, to deduce the 

 reticulated figures on the cells of the liber of the Apocynece, 

 of the parenchymatous cells of numerous tropical Orchidece, 

 superposition Dahlia tubers, &c, rather from the adcumbency 

 of two exceedingly delicate layers, formed of contrarily wound 

 spirals, than to have recourse to quite a new mode of arrange- 

 ment, which seems justified by no other peculiarity of the 

 organ or of the occurrence. But I perceive it might be diffi- 

 cult here to bring direct observation in aid. 



I may allow myself, in conclusion, some observations on 

 the direction of the spiral coils. That all the reasons ad- 

 vanced by Meyen and Link respecting the difficulty of the 

 determination do not at all affect the subject, is evident ; for 

 by reversion the relative position of two spirals is certainly 

 not altered; but even the individual spirals remain wound 

 right or left, in whatever way they are observed, of which 

 Meyen may easily convince himself on a rod figured with a 

 spiral. The being wound right or left of a spiral depends not 

 merely on a different mode of viewing it, but on an internal 

 difference in its mathematical construction. Moreover the 

 sole actual difficulty mentioned by Mohl is not of such a 

 nature that it cannot be overcome by a good microscope and 

 some practice of the observer. In general I cannot agree 

 with Mohl, that the spiral vessels principally occur wound to 

 the right ; I found some left- wound very frequently, and differ- 

 ences in various individuals of the same species. From my 

 observations up to the present time, I have provisionally abs- 

 tracted the following rule as at least very frequently valid. 

 * In all spiral formations developing cotemporaneously, (com- 

 prising in the most general meaning all secondary depositions,) 

 those which are situated immediately on one another in the di- 

 rection of the radius are wound in the same direction ; but 

 those lying immediately on one another in the direction of the 

 parallels to the periphery are wound in different directions. 

 I will only mention here, as an instance, some spiroidea from 

 Cucurbita Pepo ; and I moreover appeal to the constant cross- 

 ing of the pore fissures in contiguous parenchymatous and 

 ligneous cells when observed on sections parallel to the me- 

 dullary rays. But I must at once name, as a considerable ex- 

 ception, the peculiar short, thick, but delicate walled cells, 



