686 RECORD OF CURRENT RESEARCHES RELATING TO 



I have never succeeded in seeing this second band, even with a very 

 thick layer of solution diluted with chloroform. 



(5) Relation hetxceen the two Colouring Principles. — We will now 

 consider to what cause is due the more or less deep tint of the 

 different species of Diatomacete. 



Chance having aided me in my researches, I have succeeded in 

 gathering pure species, and comparing inter se the results obtained. 

 I found first, in March 1878, very pure Diatoma elongatum in the 

 ditches of the forest of Bondy; secondly, in May, Nitzschia tenuis 

 and linearis, with some N. sigmoidea in the watercress-beds of 

 Mitry; thirdly, in September, my friend Dr. Leuduger Fortmorel 

 brought me from Saint-Brieuc a large collection of very pure Melosira 

 nummuloides ; and fom-thly, I was able to collect in June 1879 a 

 large and very pure quantity of Navicula (^Schizonema) ramosissima on 

 the rocks of Dieppe, where, at low water, the fronds can be removed 

 one by one. 



It is the spectra obtained with the solutions of diatomine resulting 

 from these various gatherings that are represented in Fig. 54, Nos. 

 4, 5, 6, 7. 



When the colouring principles are separated by means of chloro- 

 form it is seen that the chloroform assumes a dark green colour with 

 the solutions furnished by Melosira and Navicula, whilst it only 

 acquires a pale green tint with the solutions from Nitzschia and 

 Diatoma elongatum. The spectra of the solutions furnished by 

 Melosira and Navicula show the four bands of chlorophyll, whilst 

 the solutions from the two other species only show bands I. and II. 

 The first two species, therefore, contain more chlorophyll than the 

 two others, and as they have a browner tint it must also be concluded 

 that this dark tint is caused by the abundance of the chlorophyll. 



This observation clearly shows that the plasma of Diatomaceaa 

 has not an equal capacity for chlorophyll, whilst their capacity is 

 nearly the same for phycoxanthine. Thus the relations between the 

 two colouring principles may vary enormously from one species to 

 another. This fact also confirms the opinion of M. Borscow,* that 

 the variation of colour in the different species is due to the excess of 

 one of the two pigments over the other. 



Certain diatoms often take a pale green tint without any evident 

 cause [Navicula viridis, Fragilaria virescens). I incline to the 

 oijiuion of M. Borscow, who attributes this colour to the almost 

 entire disappearance of phycoxanthine under the action of a cause 

 still unknown. 



The colour of the Diatomaceas varies sometimes in a sensible 

 manner, and especially it becomes darker towards the time of the act 

 of division, afterwards resuming its normal tint. 



It would seem, therefore, that the proportion of chlorophyll 

 increases in the plasma at the epoch at which it attains its maximum 

 of vital force. The plasma assumes a still deeper tint shortly before 

 the formation of the auxospores, but resumes its natural tint as soon as 

 the silicification of the cell is about to begin, as I have succeeded in 

 * ' Die susswas. Diatomaceen dea Siid-Westlichens Russlands,' p. 67, note 15. 



