26 Schleiden in reply to Mohl on Annular Vessels. 



sels which, when mature, are purely annular ; so that I could 

 not but believe that I had before me not mere persistent mo- 

 difications of structure, but really stages of transition, even 

 though I could not have regarded the observed forms as ac- 

 tually detected in the act of development ; not to mention, 

 among other circumstances, that the persistent ring is distin- 

 guished by the sharpness of its outline, the firmness and 

 clearness of its substance, from the yellowish gelatinous trans- 

 itory portion with its eroded and defaced margin observed in 

 the moment of dissolution. I trust now that Mohl himself 

 will be convinced of the rectitude of my assertions in these 

 particular instances. 



As regards the other forms, as they are figured by Mohl 

 f. 1 — 6, 10 (PI. I.), they do not come under the notion of annu- 

 lar vessels as defined by me in my treatise, but under that of 

 reticular formations, whose reference to one or more deformed 

 spirals is as easy or even easier than in porous organizations. 



But, in general, I might pronounce the conclusion as to 

 the mode of development from the perfect form as highly im- 

 proper, for it cannot have escaped Mohl, that, after the forma- 

 tion of the original spiral, in many cases secondary threads 

 are developed as members of union, which consist of quite 

 a different substance, since they are soluble in boihng alkali, 

 yet apparently do not differ from the spiral, and make the 

 perfect comprehension of the fundamental spiral extremely 

 difficult. I consider the part of Mohl's figure 10 marked {a) 

 as of this nature. The formntion of such secondary threads 

 is frequently observable in reticulate vessels and in some forms 

 of scalariform vessels. They occur, however, in the most re- 

 markable degree in the large purely spiral vessels of the stems 

 of Scitaminea, as in Hedychyum coronarium, Canna, ike, when 

 on their gradual decline they are filled with cells. Such a pe- 

 culiar luxuriance of the threads then takes place that the ori- 

 ginally pure spiral vessel is only distinguished from a porous 

 vessel by the perfect regularity of the pores. Moreover what 

 moves me especially to adhere still to my views, is the philo- 

 sophic necessity, in a faithful investigation of nature, to limit 

 the number of principles of interpretation so long as the im- 

 possibility of referring a phenomenon to an old principle does 

 not imperatively require a new one. 



As such in point of fact, as respects the present state of 

 science, must I now freely regard Mohl's discovery of the 

 primary development of annular organisms ; and nothing now 

 remains but to let both modes of origin stand separately by 

 each other. I by no means, however, think that such will al- 

 ways be the case. The conciliation of this schism will then 



