Foliar Ray in the Wood of the Dicotyledons. 659 



persistent leaf-traces of more luxuriant ancestors. In modern species the 

 foliar ray of the primitive aggregate type has been or is in the process of 

 being reduced, diffused, or compounded. Rapid accumulation of nutritive 

 substances, such as occurs in mature twigs of unusual vigour or in regions 

 where traumatic stimulation exists, tends to produce a reversion to ancestral 

 structure. Thus in reduced forms the foliar ray is relegated to the first 

 annual rings of vigorous mature roots and shoots. Similarly, in species 

 which have suffered reduction or diffusion, the foliar aggregate ray may be 

 recalled traumatically. Furthermore, species which possess foliar rays of 

 the aggregate or compound type under the stimulus of a slight injury 

 accelerate the ' building-up ' process. However, diametrically different 

 results are secured by slow or impaired nutrition. Under conditions of this 

 sort the reduced or diffused condition is hastened by the arrested develop- 

 ment of the primitive foliar ray. This is clearly shown in specimens of the 

 Blue Beech which have been grown under unfavourable conditions, and by the 

 fact that the common Alnus incana in the northern and colder part of its 

 range has suffered more complete reduction of the foliar aggregate ray than 

 in the warmer southern part. Arrested development due to impaired 

 nutrition occurs also in plants which possess foliar rays that are of the com- 

 pound or nearly compound type. Thus severe injuries in the oak produce 

 a reversion to primitive stages of aggregation and fusion or to the uniseriate 

 condition. 



11. Castanea and Castanopsis are reduced members of the oak family, 

 just as Alnus mollis, A. acuminata, andA.yastia must be considered reduced 

 species of the genus Alnus. 



12. Owing to the important part that the foliar ray has played in the 

 structural development of Dicotyledons, the study of its evolution and 

 reduction yields evidence significant in a natural classification of Angio- 

 sperms. 



13. A more detailed consideration of the comparative anatomy and 

 phylogeny of Dicotyledonous plants indicates conclusively that the existing 

 conceptions of the origin and development of the woody cylinder of 

 Angiosperms must be fundamentally modified to agree with actual condi- 

 tions which exist among the higher seed plants. 



In conclusion, the writer wishes to express to Major Gage, I. M.S., 

 Superintendent of the Royal Botanic Gardens at Calcutta, to Mr. G. H. 

 Cave of the Lloyd Botanic Garden at Darjeeling, and to Mr. R. S. Pearson, 

 Imperial Forest Economist at Dehra Dun, his keen appreciation of their 

 courtesy in sending valuable material of Indian plants. To Dr. Jeffrey 

 the writer is much indebted for material and kind assistance in the course 

 of the investigation, and to Mr. James Austin for assistance in photomicro- 

 graphy. 



X x 2 



