208 
D. H. S. 
of the higher animals, and the fibro-vascular skeleton of the higher 
plants. The comparison does not appear to hold very closely, for 
the vascular system (with which the author’s work almost exclusively 
deals) is, in plants, often quite distinct from the true “ skeleton ” of 
mechanical tissue, to which indeed he seldom refers. None the 
less, the value of characters derived from the vascular system is 
rightly emphasized. After recognizing the services of palaeobotany 
in drawing attention to anatomical characters, the author points 
out that what is now needed is the study of development, by which 
he understands the gradual elaboration of structure, from the young 
“ seedling ” onwards, rather than growing-point development or 
histogenesis. 
Taking the Filicales first, Professor Jeffrey gives a full descrip¬ 
tion of the ontogeny of the vascular system of Marattiaceae, 
especially in species of Danaea, and finds that it is primitively an 
amphiphloic fibro-vascular tube (siphonostele) interrupted by foliar 
gaps; here, as in Pteris aquilina, the medullary strands are a subse¬ 
quent development. He observes that the internal phloem appears 
before the medullary parenchyma “ as is commonly the case in young 
stems of Ferns with the so-called polystelic type of fibro-vascular 
arrangement ” (p. 123). Later work on Marattiacere, by Farmer and 
Hill, and by Brebner, on the whole bears out the author’s conclusions,, 
though there seems to be some difference of opinion as to the time 
of appearance of the internal phloem. 
The Osmundaceae hold a critical position in the author’s theory- 
Most obesrvers have regarded the vascular system of these Ferns 
as a single cylinder, consisting essentially of an intrastelar pith 
surrounded by a ring of primitively collateral bundles—in fact as 
belonging to the medullated-monostelic type of Van Tieghem. 
Professor Jeffrey does not recognize the existence of this type; orr 
his view the pith is an included portion of the fundamental tissue 
(a return to the original interpretation of De Baryand Sachs) while 
the collateral bundles have arisen by reduction from concentric 
strands, such as occur in “polystelic ” Ferns, the internal phloem, 
which they once possessed, having now, for the most part, disappeared. 
The same explanation is extended to the vascular system of the 
Gymnosperms and Flowering Plants generally, which he regards as 
siphonostelic throughout, but modified by the loss of internal phloem. 
As regards the Osmundaceae, the evidence for the author’s view 
rests chiefly on O. cinncunomea , in which internal phloem normally 
occurs below each bi-furcation of the stem, and occasionally appears 
