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 , Coryhis^ Carpinus, Ostrya> 

 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 : t 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 f< 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 Robur, 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. maritime^) 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 



