BUdiogicqihlcal Xoti'ces. 129 



more space than can be allotted to the whole of this review ; but 

 comparing these " families " with the " coliorts " adopted by Pro- 

 fessor lleiifrey in the ' Micrographic Dictionary,' and with the 

 " groups " of Mr. Cairuthers * in Br. Gray's ' Handbook,' we find 

 little sul)stantial dilference. 



With regard to the last family, the Actlnlscece, it has been 

 questioned whether any of the genera there included, viz. IJic- 

 tyoclia, Actiniscits, Mesocena, and Eacamjiia, ought to be included in 

 the Dicttomaceif. Dhtijocha and Mesucena have been supposed to be 

 spicules of Echinodernuita, and Encampia has been placed by Kiit- 

 zing in the JJesmidiacerp, and by Smith in the Diatomacea:. Dr. 

 Kabenhorst admits that in habit and structure they differ Avidely from 

 all Diatomacece, but he considers that, having regard to their siliceous 

 covering, they ought not to be excluded from the class. 



Dr. Itabenhorst's second class is the J'liijcochronwjihycece. It has 

 been remarked above that there will probably be no objection raised 

 to the separation of the Diatomacece from the other freshwater 

 Algae ; but the same can hardly be said of the class Fhycochromo- 

 phijcece, which can only l)e looked upon as temporary. 



The nature of phycochrom is not yet ver)' well understood. The 

 term was invented by Niigeli in his ' Einzellige Algen,' where, 

 after stating that in most of the unicellular Algtc the colouring- 

 matter is chlorophyll, he says : — 



" In other genera of unicellular Algre, especially in the Chroococcaceee, 

 the cell-contents exhibit a peculiar colouring-matter. ... It is usually 

 bluish green (verdigris-green), very often orange or brick-red ; sometimes 

 it is violet- or copper-coloui-ed, very rarely blue, yellow, or pure red."' 



Cohn, in speaking of the OsciUarinece, says that the verdigris- 

 green colouring-matter of these plants, the phycochrom of Xageli, 

 is a compound body, consisting of a green substance insoluble in 

 water, but soluble in alcohol and ether, viz. cMorophyll , and of a 

 substance (conversely) soluble in water and insoluble in alcohol and 

 ether, which he calls jihi/coci/an. 



He says that, in living cells, both colouring-matters combine to 

 form a compound colour, the phycochrom of Niigeli. Dr. Aske- 

 nasy, in his papers in the ' Botanische Zeitung'f, discusses the 

 remarkable optical properties (fluorescence and the bands of ab- 

 sorption produced in the spectrum) which are exhibited by chloro- 

 phyll, and by the colouring-matter of the i^/o/vV/<w, oi. Peltiyera canina, 

 and of Collema ; and at the conclusion of his remarks he says — 



" With regard to the names phycochrom of Niigeli and rhodophyll J 

 of Cohn, I believe that they are now superfluous; for they signify 



• Mr. Carruthers's arrangement is that of Ralfs, with some modifica- 

 tions by Meneghini, Kiitzing, and others. 



t " iieitriige zur Kenutni.ss des Chloroplivll und einigen dasselbe be- 

 gleitender Farbstofie," liot. Zeit. July 19 & 2G, 1867. 



X Cohn's " rhodophyll " is the reddish-brown colouring-matter of the 

 Floride(P. 



