56 KE VIEWS. 



to them, and medullary rays, which are further developed after the 

 manner of normal secondary thickening. Later on, the growth of 

 this secondary thickening zone ceases, and it is replaced by a new 

 one similar to it, which had already begun to appear at the outer 

 limit of the second layer of bast, in the form of tangential divi- 

 sions, which arise at scattered points, and extend thence laterally 

 all round. And since the same process is repeated, there arise in 

 the beet-root the annular markings. This short explanation is 

 condensed from De Bary's work, to which reference should be 

 made for fuller details. H. Vv^ Lett, ]\LA. 



The concentric circles in beet-root are to be accounted for by 

 the fact that the root is actually the stem of the plant, and the 

 circles are those common to stems of exogenous plants. 



E.Sc, Plymouth. 



IRcvicwe. 



Fresh-AVater Alg^ of the United States (exclusive of 



the Diatomacese), Complemental to Desmids of the United States ; with 

 2,300 ilhistiations, covering 157 coloured plates, including 9 additional plates 

 of Desmids. By the Rev. Francis Wolle, member of the American Society of 

 Microscopists. Royal Svo. Vol. I., text pp. 364; Vol. II., Plates Nos. LIV. 

 to CCX. Price $10.00. (London : Dulau and Co., 37 Soho Square.) 



We have before us two magnificent volumes, containing a vast amount of 

 most valuable knowledge. In the introductory chapter the author discusses 

 the polymorphiim of the Algre and its bearing upon the system of classifica- 

 tion, and suggests that sooner or later the whole system of classification must 

 be changed. 



In these volumes the Algae are arranged under three classes, viz. — Rhodo- 

 phycese, Chlorophycere, and Cyanophycese, and are subdivided in the following 

 manner : — 



Class I. — Rhodgi'HYCe.^;. 



Order I. — Flon'deic. Families: — I, Lemaneacere ; 2, Porphyraceae ; 

 3, Batrachospermacece ; 4, Hildebrandtiaceae. 



Class II. — Chlorophyce^. 



Order II. — Confervoidea:. Families: — 5, ColeochcetaceK ; 6, Gidogonia- 

 cere ; 7, SjihceropleaceEe ; 8, Confervacete ; 9, Pithopehraceas. 



Order III. — SipIionCiC. Families: — 10, Vaucheriacea; ; 11, Botrydiaceae. 



Order IV. — Protococcoidecv. Families: — 12, \'olvocacece ; 13, Protococca- 

 cene ; 14, Palmellaceas ; 15, Chytridiea;. 



Order V. — Zygosporeic. Families: — 16, Conjugala: ; 17, Desmidiea;. 



Class III. — Cyangphyce.^. 



Order VI. — Schizosporeic. Families: — 18, Nostocaceas ; 19, Chroococca- 

 cese. 



The descriptions, both of genera and species, are full and good ; the 

 measurements of the cells, spores, and filaments are given in micromillimetres. 

 The labour of producing these volumes must have been immense, and w^e are 



