i 5 8 SCIENCE PROGRESS 



of special groups and chapters on : Anatomical structure and climatic evolution, 

 Evolutionary principles exhibited by the Composite, together with an account of 

 the methods of anatomical technique employed at Harvard University. 



In some respects the most interesting chapters are those concerned with the 

 fibro-vascular system. These occupy nearly a quarter of the text, and much 

 detail is here incorporated in the account of the author's views regarding cor- 

 relation between the appearance of parenchymatous storage elements and the 

 secondary wood, and the phenomenon of annual rings. The formation of wood 

 parenchyma and the occurrence of tangential pitting are held to be concomitants 

 of the seasonal differentiation of the secondary xylem. Phylogenetically the wood 

 parenchyma is considered to have been derived from tracheids, and to have first 

 originated at the tangential face of the summer wood. The diffuse occurrence of 

 wood parenchyma throughout the annual ring, as also of the tangential pitting, is 

 thus viewed as a subsequent extension, leading to the extreme condition in which 

 the parenchyma is confined to the ends of the annual rings and the periphery of 

 the vessels. The radial parenchyma is similarly regarded as a derivative of 

 tracheal elements, and interesting views are advanced, in these and later chapters, 

 as to the relationships of the types of radial parenchyma in woody and herbaceous 

 Angiosperms. 



In dealing with the Lycopsida, Prof. Jeffrey advocates the view which regards 

 the pith as of cortical origin. This seems the more remarkable as emanating 

 from one who lays such stress on the primitively microphyllous character of the 

 group in question. The account of the Filicales only occupies fifteen pages in 

 spite of the large amount of comparative work in this field during recent years. 

 In a volume of this character the whole series of fossil Osmundaceous forms might 

 appropriately have been considered, however briefly. All the more as the sole 

 example described, though perhaps most favourable to the author's special views, 

 is scarcely representative of the primitive structure of the group. The earlier 

 Zalesskya and Thamnopleris, like the Lepidodendrons and Botryopterideas, 

 strongly support the evolution of a medulla of stelar origin, although there can be 

 little doubt that in more advanced types cortical incursions associated with leaf- 

 gaps augmented the pith thus formed. Prof. Jeffrey, however, appears to regard 

 the medulla as in all cases derived in the latter manner. 



The section dealing with the Coniferales is in many respects excellent and 

 affords the author an opportunity of elaborating his well-known views on the 

 primitive character of the Abietineas. The anatomical structure in this group 

 has received so much attention from Prof. Jeffrey and his school that such a 

 generalised account should prove welcome to the student. 



The author is at pains to insist on the elementary character of the work 

 and, as such, opinion will naturally differ as to what should have been included 

 and what omitted. There is, however, an obvious inequality of treatment, for 

 whilst on the one hand certain chapters are somewhat discursive and contain 

 some redundant repetitition, others, notably those on the epidermis and the 

 sporangia, are extremely brief and scarcely commensurate with the importance 

 of their subjects. 



The value of the work as an introduction to more specialised study would have 

 been enhanced by the inclusion of literature references, all the more on account 

 of the controversial character of some of the views expressed. The volume is 

 essentially one that will prove most valuable in the hands of the critical reader, 

 and for such the originality of treatment will more than compensate for any short- 

 comings that may be apparent. 



