20 CURREY, ON THE SPIRAL THREADS 



the cell-membrane is dissolved and the spiral fibre left free ; 

 I have tried the effect with the Trichia-threads, and have 

 found them either to resist the action of the acid altogether, or, 

 if the acid operated, that the threads became uniformly 

 charred, but presenting nothing to lead to the conclusion of 

 the existence of a spiral fibre. Moreover, if iodine and sul- 

 phuric acid be employed, the effect produced upon the cell- 

 wall and upon the supposed spiral fibre is the same. 



Another objection to the fibre theory appears to me to arise 

 from the unevenness or rather waviness of outline which exists 

 in almost all the threads which I liave examined, and which is 

 not usual in spiral vessel's in general ; and also from the fact 

 that the end of the supposed fibre is never to l)e seen pro- 

 truding from the cell, which might be expected when the 

 threads are ruptured as they frequently are. 



The theory of Schleiden and Schacht that the spiral ap- 

 pearance is caused by the twisting of flat band-like cells is 

 very difficult to be maintained, and I cannot help thinking 

 that they have formed their opinions from an examination 

 only of such simple threads as are represented in figs. 1 and 4. 

 It might be possible for the spiral appearance in such cells to 

 be produced by a twist, but 1 cannot conceive how the " Z)re- 

 hmiff xim sick selbst,'^ as Schacht expresses it, of the cells can 

 be called in aid to explain the spiral appearance in such a 

 thread as that of T. serpula, shown in fig, 8 ; the thing seems 

 to be mechanically impossible. 



If the above theories be incorrect, it may be asked, in what 

 other manner is it possible to account for the spiral appear- 

 ance ? Now it seems to me that it may be accounted for by 

 supposing the existence of an accurate elevation in the wall of 

 the cell, following a spiral direction from one end of the 

 threads to the other This supposition would, I think, accord 

 well with the optical appearances, and it would account exactly 

 for the undulations of outline to which I have before referred. 

 I have in my possession a thread of Trichia chrysosperina, in 

 which the spiral appearance is so manifestly caused by an 

 elevation of this nature — in which it is so clear that no internal 

 spiral fibre exists — that I do not think there could be a doubt 

 in the mind of any person carefully examining it with a power 

 of 500 diameters, that the cause of the spiral appearance is 

 not a spiral fibre. I have also a species of Arcyria, in which 

 the threads are (as in the other Arcyria) echinilate or denti- 

 culate, and the teeth appear to take a spiral direction round 

 the threads ; these teeth are mostly at a short distance apart ; 

 but at a spot where the teeth are so close as to have Ijecome 

 confluent, the appearance produced is almost precisely the 



