Vegetable Physiology for the Year 1836. 439 



instruments and under favourable light, the substance of these 

 apparent fibres appears to be exactly the same as that which 

 fills out the intermediate spaces ; and this fibrous appearance 

 seems to indicate not the existence of real separate fibres, but 

 rather a small difference in the thickness of the cellular mem- 

 brane : perhaps a different arrangement of the molecules at 

 various points, perhaps a small difference in the thickness of 

 the membrane causes a different refraction of light, precisely 

 in the same way as fibres are visible in badly melted glass." 

 Mohl also throws out the opinion that such a texture of the 

 cellular membrane is very common, as several observations 

 have seemed to prove to him. 



Valentin (I. c, p. 89) repeated these observations of Mohl, 

 and has completed them in many respects. He observed per- 

 fectly well in the cells oftheliberof Nerium odoriim, that the dia- 

 gonal or rather horizontal stripes which these cells exhibit are 

 found entirely outside, while the spirals which cross one another 

 are found in different lamellae bent over each other. And in 

 each partition of the cells these spirals always take one and 

 the same direction; and for that reason they must cross in 

 opposite partitions. Valentin observes this structure of the tubes 

 of the liber and woody cells in various other cases partly known, 

 and partly not yet noticed, and arrives at the conclusion that 

 they are all without exception lignifications, and that their par- 

 titions are never those of the primary cellular sac alone, but 

 that they are also covered with ligneous lamellae. And, as 

 Valentin had not yet found these spiral lines in the more 

 simple cells and septa (in which they however occur quite as 

 beautiful, as I can prove in several cases,) he thinks he is able 

 to consider these as the consequence of the process of lignifi- 

 cation; the history of their development even is said to remove 

 all doubt on this subject. 



Valentin at the same time gives a history of the formation 

 of the spiral stripes, which are certainly very difficult to ob- 

 serve in their formation. " In the centre of the tube of the 

 liber a very fine granular substance is perceived, the granules 

 of which possess for the most part a transversal arrangement. 

 The corpuscles of this substance at first do not allow of our 

 observing any definite arrangement. Subsequently they form 

 diagonal lines, then spiral lines, in which, however, at the be- 

 ginning it is still possible to distinguish the individual corpus- 

 cules, and which at last run on in an uninterrupted con* 

 tinuity." 



Link* has examined the seed of the Casuarince, in refer- 



* Philos. Bot.y i. p. 186. 



