INVERTEBRATA, CRYPTOGAMIA, IIICROSCOPY, ETC. 687 



proving in the specimens gathered in the pond of Saint-Cucufa in 

 February 1877. 



Besides these transient changes, the plasma usually preserves a 

 colour of its own. Thus, Navicula in general, Melosira, Pleurosigma 

 halticum, Bhabdonema, &c., present a very dark brown colour, whilst 

 Gocconeis, Nitzschia, Siatoma elonijaium, AmpMprora alata, &c., only 

 show endochrorae of a very pale yellowish-brown. 



If we examine the spectra furnished by the different solutions of 

 diatomine we shall see that the bands I. to IV. of chlorophyll appear 

 when the latter exists in larger quantity than the phycoxanthine. On 

 the other hand, the bands I. and II. only are seen, and not bands 

 III. and IV., when the chlorophyll exists only in small quantity. 

 In the latter case it is the spectrum of phycoxanthine which domi- 

 nates, because the absorption of the second part of the spectrum 

 extends to 63 and decreases to 68. 



(6) Conclusions. — It will be readily understood from the preceding 

 that certain Diatoraacea3, particularly the darkest, Melosira, Navicula, 

 &c., may become green by desiccation. In this case the jjhycoxan- 

 thine, which is very unstable . in the light, disappears first, whilst the 

 chlorophyll persists much longer. 



The green tint which the Diatomaceae take under the action of 

 acids is communicated to them by phycoxanthine, which turns green 

 when in contact with acids. 



The action of alcohol, and consequently that of glycerine, may be 

 explained by the often observed fact that phycoxanthine, being more 

 soluble in alcohol than chlorophyll, is separated from the latter, 

 which remains longer inside the frustules without dissolving. Per- 

 haps also the alcohol effects a simple molecular change in diatomine, 

 and separates, by isolating them, the yellow and green colom-ing 

 principles, which were intimately mingled. 



To sum up : the endochrome of the Diatomaceae contains a colour- 

 ing substance, diatomine, which has much analogy with the chlorophyll 

 of tlic higher plants. This colouring principle splits up into phy- 

 coxanthine and chlorophyll ; but the proportions of these two colouring 

 substances varies in different species. The Diatomaceae which are 

 the darkest in colour are those which contain the most chlorophyll. 

 Finally, the spectrum of diatomine shows a great analogy to that of 

 normal chloroi>hyll." 



Belgian Diatomaceae. — Dr. H. van Ileurck, of the Botanic 

 Garden of Antwerp, has published, with the aid of Hcrr A. Grunow, 

 the 1st part of a Synopsis of the Diatomaceae of Belgium, which 

 will consist of 6 parts, with heliographic plates. (Parts 1 and 2, 

 Ilaphidea3 ; Parts 3 and 4, Pseudo-Rai)hiderc ; Parts 5 and 6, Crypto- 

 Raphidcae.) Tlio author points out the favourable situation of Belgium 

 as regards these Algae : the North Sea coast furnishing nearly all the 

 marine species described by English observers ; the Ardennes, a f ooil 

 number of the European Alpine species, and tlio central parts of 

 Belgium, the fresh-water species forming the foundation <if the 

 European flora. 



In liis preface the autlior says tliat all the drawings have bfcn 



