378 Mr. J. Ralfs on the British Desmidiea;. 



observations, but with regard to those on the action of iodine he 

 says, " I cannot otherwise account for Mr. Dahymple's statement, 

 that iodine ' in no instance produced in the Closteria the violet or 

 blue colour indicating starch/ than by supposing that the speci- 

 mens 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 ex- 

 periments to confirm 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 ac- 

 tion of this reagent, that the purple colour of the granules can 

 only be detected after crushing the specimen by means of the 

 compressor. The characteristic colour of iodide of starch is then 

 shown most distinctly. I have repeatedly treated in this way Clo- 

 sterium Trahecula as well as others, and have uniformly found that 

 a portion of the interior takes the purplish colour.^' 



Professor Bailey, however, does not ^' consider the presence of 

 starch in these bodies as conclusive evidence that they are plants;" 

 for he suggests with some ingenuity, " Is it not possible that they 

 are animals which feed, wholly or in part, on amylaceous matter 

 extracted from the aquatic plants among which they live ? If so, 

 the detection of starch in their stomachs is not surprising." 



Having been indebted to Mr. Dalrymple for much information 

 respecting this tribe, and invariably found his observations most 

 accurate, I was puzzled how to reconcile these contradictory re- 

 sults of the test of iodine ; I have therefore repeatedly and care- 

 fully noted the effects of iodine on many of the Desmidiece. 



In a young state the cells are filled with a green homogeneous 

 fluid, which, as the plant approaches to maturity, becomes denser 

 and minutely granular. Scattered amongst this minutely granu- 

 lar matter larger granules make their appearance ; these Ehren- 

 berg calls ova; but I cannot perceive the slightest difference 

 between them and the granules present in the higher Algse, and 

 Meyen informs us that he " had observed their development into 

 spores." 



On applying diluted tincture of iodine to different species of 

 the Desmidie(2y these large granules became very dark with a pur- 

 plish tinge, showing the presence of starch. When the tincture 

 of iodine is used in its undiluted state, the colouring matter be- 

 comes so dark as to appear nearly black and conceal the bluish 

 tint ; in some specimens too this colour is hardly perceptible, 

 whilst in others it is very apparent. 



In no instance have I found the presence of starch indicated 

 unless these granules were present, as the fluid colouring matter 

 always becomes brownish. The application of iodine to Conju' 



