32 INTRODUCTION. 



of granular matter, the fact of blue granules in some is how- 

 ever decisive of the presence of starch." Mr. Dalrymple is 

 so careful and accurate an observer, that I doubt not his 

 failure was caused by the immature state of the specimens 

 on which he experimented, as he indeed subsequently allowed 

 might have been the case. 



Professor Bailey of the U.S. Mihtary Academy, in an 

 article on the American ' Desmidiaceae'*, gives copious ex- 

 tracts from Mr. Dalrymple's paper on the Closteria, accom- 

 panied by his own remarks. He bears testimony to the 

 general correctness of Mr. Dalrymple's observations, but 

 with regard to those on the action of iodine, he says, "I 

 cannot otherwise account for Mr. Dalrymple's statement, 

 that iodine ' in no instance produced in the Closteria the 

 violet or blue colour indicating starch,' than by supposing 

 that the specimens he examined were not in the proper 

 state to exhibit it. Meyen expressly states that it is * at 

 certain times, particularly in spring,' that the starch may 

 be detected. I am able by conclusive experiments to con- 

 firm Meyen's statement as to the presence of starch in 

 these bodies. In specimens gathered in November I find 

 no difficulty in producing the blue colour with tincture of 

 iodine. Sometimes however the specimen becomes so 

 opake by the action of this reagent, that the purple colour 

 of the granules can only be detected after crushing the spe- 

 cimen by means of the compressor. Tlie characteristic colour 

 of iodide of starch is then shown most distinctly. I have re- 

 peatedly treated in this way Closterium Trabecula, as well as 

 others, and have uniformly found that a portion of the in- 

 terior takes the purplish colour f." 



I have myself repeatedly noted the effects of iodine on 

 many of the Desmidiese. In a young state the cells are filled 

 with a green homogeneous fluid, which as the plant ap- 

 proaches to maturity becomes granular. Scattered amongst 



* American Journal of Science and Arts, vol. xli. p. 287. 

 t Ibid, p. 301. 



