5-i REVIEWS. 



slits, reticulations, etc., on the walls of cells is expounded in 

 a masterly and convincing way. Mohl maintains (p. 28), as 

 he has done in the " Botanische Zeitung," that cellulose forms 

 the basis of all vegetable membranes in the higher plants, and 

 that what Mulder regarded as peculiar compounds are com- 

 binations of cellulose with foreign infiltrated deposits, which 

 interfere with the chemical reactions of cellulose, but which 

 may be removed by previous maceration in caustic potash and 

 nitric acid. He now maintains, in opposition to his early 

 views (still defended by Schleiden), that the intercellular sub- 

 stance is a product or secretion of the cell, and not a univer- 

 sally distributed mass in which the cells are imbedded (p. 33). 

 He shows that the thickened " cuticle " of Unger, Mulder, 

 Harting, etc., consists of secondary layers of cell-membrane, 

 deposited from the inside, and infiltrated with some substance 

 that is colored brown by iodine ; with the exception of an 

 extremely thin external pellicle, the real cuticle of Brongniart, 

 which is probably a secretion from the surface of the cell, like 

 that which forms the outer coat of pollen-grains (p. 35). 

 He insists that the layer of protoplasm, his primordial utricle, 

 lining the cell is a soft and delicate membrane, and not a mere 

 layer of mucilage (p. 37) ; the mode in which this is con- 

 structed and a partition formed by an inward growth at the 

 fold, in the multiplication of cells by division, is very clearly 

 explained (p. 50-53). Free cell- formation is said to occur, 

 in Phaenogamous plants, only in the embryo-sac, in which both 

 the embryonal vesicle, or rudiment of the embryo, and the 

 cells of the albumen, originate in this manner; in the Crypto- 

 gamia, only in the formation of spores in certain cases, as in 

 the Lichens (p. 58) ; contrary to the view of Schleiden, who 

 long maintained this to be the universal, and lately a general, 

 mode of cell-production. Schleiden's original account of the 

 process of the formation of a free cell from a nucleus is 

 directly controverted in all essential points ; the nucleus, ac- 

 cording to Mohl, being always central, and at no time con- 

 nected with the cell-membrane, but always enclosed in the 

 primordial utricle. A nucleus, or mass of nitrogenous sub- 

 stance, first has the primordial utricle, or nitrogenous mem- 



