42 



Dr. M. J. Schleiden's Observations on 



tion ; but instead of observing their development into rings, 

 many have only inferred that the annular vessels were of far 

 later origin. Moreover, the formation usually proceeds, at 

 the moment when the bud comes to development, so rapidly, 

 that the observation of the intermediate stages is rendered 

 almost impossible by it. For obtaining a successful result 

 everything here depends on finding a plant in which all these 

 difficulties exist in a slighter degree, and on which therefore 

 the process may be accurately observed ; if once a clear in- 

 sight has been acquired in this way, it is easy to find oneself 

 at home, even with the more difficult plants. I found for these 

 inquiries the Campelia Zanonia, Rich, (frequent in most hot- 

 houses), and the subterranean stem of Equisetum arvense most 

 advantageous. 



If the very youngest internodes of the buds of the first- 

 mentioned plant be examined, a single extremely delicate and 

 densely- wound spiral vessel is found in all the as yet scarcely 

 limited vascular bundles. In older internodes the convo- 

 lutions of this vessel are found further distant from one an- 

 other, and near it exteriorly a new-formed narrow-threaded 

 spiral vessel. But if we consider in this period the first 

 formed vessel more accurately, Plate (fig. 11.), it will be seen 

 that all convolutions are not separated in the same manner from 

 one another, but that almost in regular alternation two en- 

 tire coils adhere firmly together, and one convolution is drawn 

 out. In still older internodes the extension is found to be 

 so far advanced, that the free coil loosened from the cellular 

 membrane frequently reaches as a mere band with a steep 

 ascent- from the one ring formed of two closed convolutions to 

 the other. On still further developed vessels this elongated 

 coil is seen corroded by the reabsorbing action of the cell, and 

 all the stages of transition, as they are represented in the 

 Plate (from fig. 1 to 5,) are frequently found in the continuity 

 of a single vessel. Lastly, on still older vessels, the connect- 

 ing coil is already perfectly dissolved ; but there may still be 

 observed on the isolated rings the extremities of the previous 

 spiral fibre (fig. 6, 7? Even on highly developed vessels, 

 we still find on the perfectly closed and smoothened rings, 

 their composition of two coils now and then indicated by 

 single delicate dark lines (fig. 8 — 10.). Exactly the same 

 process may likewise be easily followed in the subterranean 

 stems of Equisetum arvense ; and in particular we frequently 

 find long streaks in vessels modified as is represented in fig. 1 1 . 

 as the first stage of transition to the formation of rings. 



I must still mention another point respecting which I do 

 not at present agree with M. Mohl ; it relates to the succes- 



