ON THE EXISTENCE OF CELLULOSE IN ASCIDIANS 223 



to the primordial substance of the plant. The cellulose is deposited 

 outside both. The amount of nitrogenous matter mixed up with the 

 cellulose deposit appears to be a mere question of degree — and the 

 nature and existence of an intercellular substance in the vegetable 

 kingdom are still matters too much disputed to be good grounds of 

 distinction. 



The phsiological theory of Lowig and Kolliker, that the cellulose 

 of the Ascidians is derived from the Diatomaceje upon which they 

 feed — is incompatible with the fact (Annals of Nat. Hist, Aug. 1852) 

 that the larval Ascidian contains cellulose before any of its organs are 

 developed. 



To examine the test of an Ascidian for cellulose, I find the best 

 way to be, to take a very thin section, and moisten it with a strong 

 solution of iodine in iodide of potassium. After being thoroughly 

 impregnated with the iodine, the superfluous fluid should be drained 

 off, and the segment carefully blotted with the finger [or hair pencil]. 

 A handkerchief or blotting-paper may readily give rise to error by 

 leaving behind small fragments of vegetable fibre. A drop of sul- 

 phuric acid, as strong as can be procured, should now be added. If 

 much cellulose is present, a deep-blue colour will appear immediately, 

 beginning at the edges of the slice ; if there be but little, the colour 

 will not appear for some time. The application of the test requires 

 some care ; and while its success is most valuable evidence of the 

 presence of cellulose, its failure is not by any means negatively con- 

 clusive, unless the experiment has been frequently and carefully 

 repeated. 



