HISTORY OF DIATOMS. 5 



It contains a certain number of pyrenoids ( J ) (five or more), which 

 when the band is seen on the side, have the appearance of rounded 

 elevations of lenticular form. 



The endochrome, as already stated, consists of chlorophyl and 

 phycoxanthin, and serves the sams purpose in diatoms' as chlorophyl 

 in higher plants. Mr. P. Petit published in the " Brebissonia," of 

 January, 1880, an interesting article 0:1 the chemical and spectroscopic 

 properties of the endochrome. The result of this study can be summed 

 up in a few lines as follows : 



The colour of the endochrome varies from pale yellow to deep brown. 

 It loses it colour neither in cold nor boiling water, but it is completely 

 decolourised by macerating it for a short time in cold alcohol, which 

 latter acquires a fairly dark brownish green tint. The colouring matter 

 of the endochrome is Diatomine. This may be split up into phycoxanthine 

 the yellow, and chlorophyl or the green colouring element. 



The proportion of these two colouring matters varies according to the 

 species and the different tints of the endochrome. The darker the endo- 

 chrome, the more chlorophyl is present. To separate the constituent 

 elements of diatomine, Mr. P. Petit macerated diatoms in alcohol at oVC, 

 and diluted the product obtained with an equal volume of distilled water, 

 so as to diminish the power of the alcohol ; the solution is quite free 

 from sediment. A quantity of chloroform, equal to one-third of the whole 

 volume, is added to the mixture. After shaking it for a minute or two 

 it is allowed to rest. Seven hours afterwards the separation is complete ; 

 the chloroform assimilates the green colouring element and sinks to the 

 bottom of the flask, while the yellow colouring element, being more 

 soluble in weak alcohol, remains in the supernatant liquid. After decanting, 

 a second washing with chloroform is made, proceeding as before. 



As a rule, the second washing is sufficient to get rid of all that 

 remains of the green colouring element. If the supernatant liquid be 

 not quite clear it on be rendered so by pouring into it a small quantity 



( l ) The words chromatophore and pyreno'id were introduced as scientific terms by Fr. 

 Schmitz {Die Chrotnatophoren der A.gen ; Vergleichende Untersuchungen i/'ber Bau und 

 Ent-wicklung der Chlorophvllkorper und der Analogcn FarbsioffkSrper der A /gen, 8vo, 1S0 pp., 

 and one plate, Bonn, 1882). 



According to Fr. Schmitz the term chromatophore includes chlorophyll-bodies, coloured 

 pigments (other than green), and similar colourless bodies belonging to Algre. Otto 

 Miiller was the first to apply this term to the endochrome of diatoms. 



Pyrenoids are inclosures (characteristic in certain groups of the algae) of a colourless and 

 very refractive substance, whose re-actions, especially with staining re-agents, are similar 

 to those of the dense matter (the chromatine of Flemming and nuclear substance of Strasburger) 

 which forms a part of the nucleus of vegetable cells. 



Pyrenoids are usually globular, and in the green algae are frequently surrounded with starch. 

 Chromatophores and pyrenoids multiply by fission ; sometimes, "though rarely, pyrenoids 

 spring into existence spontaneously. 



