Bibliographical Notices. 341 



alluded to. The " Outlines " are confined entirely to structural and 

 physiological botany without reference to classification. They con- 

 tain many interesting original observations, and they give a con- 

 densed view of the state of botanical knowledge at the present time, 

 to the exclusion of all theories which have been abandoned or ad- 

 vanced without sufficient grounds. The book is thus confined within 

 a moderate compass, and the student is at once put in possession of 

 the great leading facts of the subject unencumbered with the state- 

 ment of numerous opinions. 



The author commences with a consideration of the chemical con- 

 stituents of vegetables, and then proceeds to the elementary struc- 

 ture, or the cells and vessels of plants and their functions. His re- 

 marks on cytogenesis are well worthy of attention. There are three 

 theories of cell- development which he considers worthy of notice : — 



" 1. The formation of free cells from nuclei, in the cavity of the 

 parent-cell : this view was proposed by Schleiden. 



** 2. The formation of new cells by the division of the mucilaginous 

 investment of the interior of the cell (primordial utricle) into two or 

 four perfect, closed sacs, around and by the whole outer surface of 

 which a new layer of membrane is simultaneously formed for each 

 portion, these constituting the new cells. This is the theory of 

 Nageli. 



"3. The gradual division of the primordial utricle into two por- 

 tions by an annular constriction and infolding, the fold growing in- 

 ward to the centre, and a layer of permanent cell-membrane being 

 also deposited by each lamella of the fold, gradually from the cir- 

 cumference to the centre. This view was advocated by myself as 

 the universal mode of cell-formation, in a paper read before the Bri- 

 tish Association at Cambridge last year, and has been more fully 

 developed in a recent memoir by Mohl." 



In speaking of the functions of what have been called milk-vessels 

 he says, "They may be regarded as intercellular passages containing 

 peculiar secretions not essential to the life of the plant. The pre- 

 tended circulation of the latex was a groundless hypothesis and arose 

 from erroneous observation." He thus differs completely from 

 Schultz, and believes with Mohl, that the gravitation of the fluids 

 when the vessels are cut is the cause of the motions observed. In 

 treating of the mode in which woody matter is formed, he seems to 

 discard the theories of Petit Thouars and Gaudichaud as reared on 

 erroneous foundations. At p. 54 he remarks, " Each vascular bundle 

 (of a monocotyledonous stem) originates at the point where the new 

 leaf or phyton is developed out of the nucleus of cellular tissue at the 

 apex in the centre, and is gradually elongated into an ascending por- 

 tion which passes upward into the petiole, and into a descending 

 portion which passes outward and downward a little above the 

 ascending bundle of the leaf below. It must not be imagined how- 

 ever that the descending fibres break through the cellular tissue ; no 

 interruption of continuity takes place within the stem ; the vascular 

 bundle is formed out of cells in the place where it is subsequently foundy 



