440 Prof. Meyen's Report of the Progress of 



ence to the cells which are situated under the testa, and are 

 regarded as a layer of spiral tubes which are easily unrolled. 

 Link found under these another layer or membrane consisting 

 of long parenchymatous cells, which are closed at one end, 

 and contain fibres just beginning to be evident ; but at the other 

 end are spiral fibres which became true spiral vessels. On 

 this ground Link has advanced the opinion that the cellular 

 membrane changes with age into spiral fibres ; this is repre- 

 sented in Plate III. fig. 3. of his work. I have on the con- 

 trary, in my recent work on Vegetable Physiology, endea- 

 voured to confirm the opinion that the cellular membrane is 

 composed of fibres having a spiral course. 



In a second memoir by Valentin* the structure of the cel- 

 lular membrane in reference to its lamellar structure, and 

 in regard to the form of the dots [Tupfel) is more closely ex- 

 amined. 



The thickening of the cellular membrane by the deposition 

 of new layers is called by Valentin the process of lignification, 

 and in the first stage only of development of this process do 

 the first deposited lamellae lie close on the entire surface of 

 the primary sac partition. Subsequently, however, at the end 

 of the individual development of the porous cells and vessels, 

 a circular gap is formed around the exterior limit of the porous 

 canal (Tupfelkanal dotted duct) between the first super- 

 posed layers of lignification, and the primary sac partition 

 whose exterior periphery runs in a direction concentric with 

 that of the porous canal, and which gradually becomes small- 

 er from this point up to its circumference, until both 

 membranes become once more fixed close to each other. 

 The porous canal as well as the gap above cited constantly 

 contained, like the interior of these ligneous cells or vessels, 

 an aeriform substance. Valentin then gives a more 

 accurate description of the great disks with double circles 

 which the cells of the Coniferce exhibit, and accompanies 

 his explanation with some figures, from which it is evident 

 that some error has occurred in these observations ; for it is 

 very easy to perceive in these formations a coincidence with 

 the structure of other dots ; while Valentin's representation 

 is quite at variance with this. For according to it, next to 

 the external layer of the cellular membrane is situated a 

 great gap, which is said gradually to contract into a fine 

 passage representing a dot, and to merge into the cavity of the 

 cell ; while, according to the observations of other botanists, 



* On the various forms of the porous canal in the porous cells and ves- 

 sels.— Vide his Repert., $c. t p. 78—87- 



