650 Bailey. — The Evolutionary History of the 
of normal mature plants, but in addition an intensive study is necessary of 
the development of structures during the life-history of individual plants. 
Such developmental studies should be made to cover numerous species 
selected from as many genera and families as possible. Furthermore, 
since ancestral characters are known to persist in the seedling, reproductive 
axis, leaf, and first-formed portion of vigorous mature shoots of plants 
which have suffered vegetative reduction, and to be recalled in traumatic 
regions of plants which have been similarly reduced, it is essential that 
these regions be examined with particular care. Finally, palaeobotanical 
material, when available, must be regarded as an invaluable check upon con- 
clusions of phylogenetic significance reached from living material. 
It is unfortunate that Professor Groom’s conclusions are based upon 
rather narrow foundations. The material used by him consisted evidently 
almost exclusively of mature oak wood, a large part of which was composed 
of American species cut from a collection in the possession of this Laboratory. 
An extensive study of the development of ray structures in the life-history 
of different species of oak (such as was made by Eames in the case of certain 
vines and species of the Rosaceae, Ranunculaceae, and other families, and 
by the writer in the case of many species of the following genera of the 
Fagales, Quercus, Pasania , Alnus , Be tula, Corylus , Carpinus , Os try a, 
Castanea , Castanopsis , and Fagus ) was not attempted by Professor Groom. 
Nor did he examine those regions of the plant which retain ancestral 
characters. 
In view of these facts certain criticisms by Professor Groom of the 
results secured by Eames and the writer are of interest. Professor Groom 
states : ‘ From the point of view of the assumption that the seedling is a seat 
of phylogenetically early structure features, these facts lose their significance 
if it be shown that a similar linking up ” of small rays to form large ones 
takes place in older parts. I find that such a “ linking up ” does take place, 
at least in connexion with some of the rays of the inner rings of the twigs 
of Quercus Rofoir , L.’ 
It is necessary at this point to emphasize the important fact that the 
foliar ray has reached varying stages of aggregation and fusion in different 
species of the Fagales. In Alnus japonica^ Sieb. et Zucc., A. rhombifolia , 
A . maritima, and many evergreen oaks the foliar ray is of the aggregate type 
composed of congeries of smaller rays more or less imperfectly fused. The 
first-formed wood of the seedling possesses solely uniseriate rays, and the 
development of foliar rays is a progression in the direction of compounding. 
In most oaks with a distinctly deciduous foliage and in certain somewhat 
ring-porous evergreen oaks from the western and south-western part of the 
United States, the foliar ray is of the compound type> composed largely 
of a nearly homogeneous mass of parenchyma. In the highest types of 
this group the fused or compound condition of the foliar ray occurs except 
