Mr. J. Ralfs on the British Desmidiese. 379 



(/ata m different stages of growth was followed by a precisely si- 

 milar result. In the young plant no starch was detected, but the 

 colouring matter became changed to an orange-brown. On the 

 other hand, in the conjugated filaments the granules became blue, 

 and the spores especially appeared of the very dark colour often 

 observed in the Desmidiea, and did not exhibit any blue tint until 

 they were crushed*. As the large granules are not present in 

 the early state of the plant, and as it has been shown above that 

 they alone contain starch, the opposite results of the experiments 

 by Meyen and Mr. Dalrymple may be thus explained f. 



In the preceding remarks I have classed the Closteria with the 

 DesmidiecE. Ehrenberg indeed describes them as a distinct family, 

 but his opinion has, I believe, very few advocates. Meyen says, 

 " I see no good reason why Closterium should not be placed near 

 Euastj'um /^ and Professor Bailey says, " I have before stated that 

 I consider the genus Closterium most closely related to Euastrum, 

 and therefore to the Desmidiacece generally. This relation to 

 Euastrum is manifest in their apparent identity in internal struc- 

 ture ; the chief difference between them is only in the external 

 forms ; and even in them we find there is a perfect transition 

 from the highly-lobed and tabular forms of some species of Eu- 

 astruMj to the entire, elongated and fusiform species of Closterium. 

 It is therefore without hesitation that I place Closterium (as in- 

 deed most writers do) among the Desmidiacece. '^ 



I am aware the following account of the British Desmidiea 



* I would advise those who wish to repeat the experiments, and have no^ 

 been accustomed to see the effect produced on starch hy the application of 

 iodine, to apply it first to a few grains of flour, and afterwards to some spe- 

 cies o^ Zygnema in which the spores are about to form ; as they will thus 

 become familiar with the appearance of iodide of starch when formed in the 

 Algae. 



After the tincture of iodine is applied let them add a little more water, 

 and then dry the specimen by the application of heat; this will drive off' the 

 free iodine, and thus in a gi-eat measure remove the brownish stain which 

 obscures the purple tint. They should then add a drop of water, and on ap- 

 plying the highest power of the microscope the peculiar colour of the iodide 

 of starch can in general be easily perceived. 



\ I have the satisfaction to add, that since I wrote the present paper I 

 communicated the tenor of it, with accompanying specimens of Closterium 

 digitus, to Mr. Dalrymple, who acknowledged the presence of iodine in the 

 following terms : — ** I have examined the specimens sent up, and in several 

 I can detect the blue colour of the iodide of starch : this is by no means 

 however universal, some being merely stained yellowish brown ; but in those 

 instances there appears to be an absence of granular matter-, the fact of blue 

 granules in some is however decisive of the presence of starch." He also 

 says, " I am glad to see your explanation of the facts. It is a probable cir- 

 cumstance that iodine may act differently at different stages of growth, and 

 that starch may not always be present in the specimens." 



Mr. Jenner also informs me that he has repeated my experiments with 

 success. 



