NOTICES OF BOOKS AND MEMOIKS. 221 



into an inner and two outer cells. By this means a second small 

 square is formed inside the central square. The four cells con- 

 stituting this small square divide each by three longitudinal 

 divisions perpendicular to each other ; while each of the outer 

 cells divides radially, and the daughter-cells are each of them 

 segmented into three by two periclinal walls. The peripheral layer 

 forms the spore-layer (as in the species before examined). The 

 further multiplication of the cells of these layers takes place 

 radially. The formation of the au'-chamber is essentially the same 

 as in Phascum. Whilst the cells of the inner layer of the wall 

 swell up and assume a rounded form, the greater number of the 

 cells become separated from the layer outside and inside them, and 

 only in single places do they remain in connection either with the 

 layer inside or outside them. Thus arise the two- to five-celled 

 threads which connect the capsule- wall with the outer spore- sac. 

 These threads are, at first, dii'ected from above downwards and 

 outwards ; afterwards they are almost horizontal. 



The portion of the paper occupied with the development of the 

 embryo of PolypodiacecB is copiously and very clearly illustrated, 

 but it does not call for special remark. 



The author then passes on to criticise Pringsheim's objection to 

 his theory of revolution of the embryo ; this objection is founded 

 on the presumed fact of the seta being an axial structure, a view 

 which is energetically denied. 



S. M. 



Botany; Moryholoqij and Physiology. By W. E. M'Nab, M.D., 



F.L.S. 

 Botany: Classification of Plants. By W. K. M'Nab, M.D., F.L.S. 

 (London Science Class-Books. ) Longmans & Co. 1878. 



These two small volumes are intended to serve conjointly " as 

 a basis for the botanical teachmg in the higher classes of schools, 

 and also to supply the wants of medical and other students." 

 The plan pursued is essentially different from that followed in 

 most of the English elementary works on Botany at present in 

 use, of which we may take Su' J. D. Hooker's " Primer of Botany " 

 as the best exponent. Instead of occupying the attention of the 

 beginner for the most part with details of the morphology of the 

 various organs, and with the technical terms thus brought into use, 

 Professor M'Nab plunges at once into the heart of his subject, and 

 describes, in the first few pages, the structure of the histological 

 cell, proceeding next to that of tissues. The plan is, in miniature, 

 the same as that of Sachs's "Lehrbuch," and, mdeed, of almost 

 all German text-books. We believe it to be sound; and oiu: own 

 experience convinces us that it is the right course for young, as 

 well as for more advanced, students. The two volumes form 

 together, in fact, very much a condensed abstract of the fourth Ger- 

 man edition of Sachs's Textbook, which has not yet appeared in an 

 English dress, and which contains many material changes fi-om 

 the third. The chapters on Morphology and Physiology seem to us 



