THE 
HEW PHYTOliOGIST. 
Vol. i., No. 2. February 19TH, 1902. 
THE OLD WOOD AND THE NEW. 
By D. H. Scott, F.R.S. 
rnHE appearance of secondary wood and bast, with power of 
indefinite increase by means of cambium, was the most 
important event in the anatomical evolution of the vascular plants. 
We now know that this advance was made exceedingly early, and in 
many lines of descent; at the commencement of the Carboniferous 
epoch, we find secondary growth well established in every group of 
Vascular Cryptogams, as well as in the Gymnosperms which had 
already sprung from them. 1 Its common occurrence among the 
Pteridophytes of Palaeozoic age—a result which we owe in great 
measure to the discoveries of Williamson—is specially interesting, 
because their representatives at the present day have, for the most 
part, lost this power. 
The object of the present article is to trace briefly, in one 
series of forms, some of the structural changes induced by the 
introduction of secondary growth, confining our attention to the 
wood, which, from its good preservation in fossil plants, is best 
suited for our purpose. It is proposed to follow the competition, if 
we may so call it, between the new Phanerogamic secondary wood? 
and the old Cryptogamic primary wood, which the former first 
supplemented and then displaced. The phrases Cryptogamic and 
Phanerogamic wood are due to the French school of palaeo- 
hotanists, who applied them, in the first instance, to the centripetal 
and centrifugal wood, so sharply contrasted in the stems of fossil 
Lycopods. The distinction is valuable and suggestive, even though 
the series to which the French authors applied it be not that which 
actually led up to the higher plants. Centripetal wood is not, of 
course, limited to Cryptogams, nor centrifugal to Phanerogams—if 
it were so, any evolutionary sequence would be out of the question— 
but each may be taken as characteristic of its class; as we approach 
>We are not here concerned with secondary growth in other than 
vascular tissues (e.g.: periderm) or in other than vascular 
plants (o.g.: stipe of Laminariaceous Algae). 
