394 YOUNGKEN— ON THE MYRICACEAE 



10. The author shows that from the seedhng primary root of five to 

 six months growth and from thence onward characteristic root tubercles 

 are formed in the above named two species and their hybrid. The or- 

 ganism is found in all these to be an Actinomyces (here first described 

 as Actinomyces myricarum of the author) that abundantly fills infested 

 cells in the cortex of the tubercles, which owe their origin as arrested 

 and modified roots to its irritant and invading action. As a result 

 of cultures made from tubercles, the author concludes that good cultures 

 of the organism can be secured on nutrient agar. 



11. Since Actinomyces is frequently a virulent pathogenic organism 

 in cattle and other domestic animals up to man, the author suggests 

 the possible pathogenic relation of the Myrica organism to such animals. 

 He, therefore, would regard the infesting organism as parasitic in relation. 



12. In Comptonia asplenifolia, a similar Actinomyces organism is the 

 primary infecting agent, but there often appears a mycelium producing 

 fungus probably belonging to the Oomycetes. 



13. As for the roots so for the stems of M. cerifera, M. Carolinensis 

 and the hybrid, a careful comparative histological study has been made 

 and details recorded as to the resemblances and differences of the hybrid 

 and its parents. During this study obUque barred septa have been 

 discovered separating the pitted vessels from each other. 



14. Coccus-hke forms that the writer believes to be involution forms 

 of the infesting Actinomyces have been discovered in the cavities of the 

 pitted vessels. Such seem to indicate the pathway of infestment taken 

 by the Actinomyces in order ultimately to reach the fruit wall. 



15. In the study of the leaves new structural details have been 

 observed, but special interest attaches to the presence now recorded of 

 orange-red bowl to saucer-shaped glandular hairs specifically character- 

 istic of M. cerifera and in a reduced degree of M. Macfarlanei intermingled 

 with golden-yellow glandular hairs of Chevalier. The latter only are 

 present in M. Carolinensis. The hybrid, moreover, in general histology 

 is shown to be more or less intermediate between the parents. 



16. The last named conclusion regarding the hybrid and its parentage 

 is further verified by comparative studies recorded for the stem and root. 



17. Exact phytophenological records have been made as to the 

 maturation of the floral parts and the period of blossoming in April and 

 May. 



Spore mother cell formation is completed by autumn of one year, 

 but formation of tetrads proceeds in the dififerent species studied from 

 mid April to mid May in the Philadelphia neighborhood. 



